Method and apparatus for uplink channel access in a high efficiency wireless LAN

ABSTRACT

The present disclosure relates to a method and apparatus for uplink channel access in a High Efficiency WLAN (HEW). According to one aspect, a method for transmitting an uplink frame by a station (STA) to an access point (AP) in a wireless local area network may be provided. The method may include receiving from the AP a trigger frame for eliciting an uplink transmission from the STA, transmitting to the AP the uplink frame according to a type of the trigger frame, wherein when the uplink frame is transmitted in an uplink multiple user (MU) transmission, the uplink frame includes a padding added by the STA such that transmissions from a plurality of STAs including the STA in the uplink MU transmission end at a same time indicated by the trigger frame, and receiving from the AP a frame in response to the uplink MU transmission a predetermined time after an end of the uplink MU transmission.

This application is a continuation of U.S. patent application Ser. No.14/885,881, filed on Oct. 16, 2015, now U.S. Pat. No. 9,854,606, toissue on Dec. 26, 2017, which claims the benefits of U.S. ProvisionalApplication No. 62/064,785, filed on Oct. 16, 2014, U.S. ProvisionalApplication No. 62/069,662, filed on Oct. 28, 2014, and U.S. ProvisionalApplication No. 62/083,855, filed on Nov. 24, 2014, which are herebyincorporated by reference as if fully set forth herein.

BACKGROUND Technical Field

The present disclosure relates to a Wireless Local Area Network (WLAN),and more particularly, to a method, apparatus, and software for uplinkchannel access in a High Efficiency WLAN (HEW), and a recording mediumthat stores the software.

Related Art

Along with the recent development of information and telecommunicationtechnology, various wireless communication techniques have beendeveloped. Among them, the WLAN enables a user to wirelessly access theInternet based on radio frequency technology in a home, an office, or aspecific service area using a portable terminal such as a PersonalDigital Assistant (PDA), a laptop computer, a Portable Multimedia Player(PMP), a smartphone, etc.

To overcome limitations in communication speed that the WLAN faces, therecent technical standards have introduced a system that increases thespeed, reliability, and coverage of a wireless network. For example, theInstitute of Electrical and Electronics Engineers (IEEE) 802.11nstandard has introduced Multiple Input Multiple Output (MIMO) that isimplemented using multiple antennas at both a transmitter and a receiverin order to support High Throughput (HT) at a data processing rate of upto 540 Mbps, minimize transmission errors, and optimize data rates.

In recent times, to support increased numbers of devices supportingWLAN, such as smartphones, more Access Points (APs) have been deployed.Despite increase in use of WLAN devices supporting the Institute ofElectrical and Electronics Engineers (IEEE) 802.11ac standard, thatprovide high performance relative to WLAN devices supporting the legacyIEEE 802.11g/n standard, a WLAN system supporting higher performance isrequired due to WLAN users' increased use of high volume content such asa ultra high definition video. Although a conventional WLAN system hasaimed at increase of bandwidth and improvement of a peak transmissionrate, actual users thereof could not feel drastic increase of suchperformance.

In a task group called IEEE 802.11ax, High Efficiency WLAN (HEW)standardization is under discussion. The HEW aims at improvingperformance felt by users demanding high-capacity, high-rate serviceswhile supporting simultaneous access of numerous stations in anenvironment in which a plurality of APs is densely deployed and coverageareas of APs overlap.

However, there is no specified method for uplink channel access in aHEW.

SUMMARY

Objects of the present disclosure is to provide a method and apparatusfor uplink channel access in a High Efficiency WLAN (HEW).

The objects of the present disclosure are not limited to the foregoingdescriptions, and additional objects will become apparent to thosehaving ordinary skill in the pertinent art to the present disclosurebased upon the following descriptions.

In an aspect of the present disclosure, a method for transmitting anuplink frame by a station (STA) to an access point (AP) in a wirelesslocal area network may be provided. The method may include receivingfrom the AP a trigger frame for eliciting an uplink transmission fromthe STA, transmitting to the AP the uplink frame according to a type ofthe trigger frame, wherein when the uplink frame is transmitted in anuplink multiple user (MU) transmission, the uplink frame includes apadding added by the STA such that transmissions from a plurality ofSTAs including the STA in the uplink MU transmission end at a same timeindicated by the trigger frame, and receiving from the AP a frame inresponse to the uplink MU transmission a predetermined time after an endof the uplink MU transmission.

In another aspect of the present disclosure, a method for receiving anuplink transmission by an AP in a wireless local area network may beprovided. The method may include transmitting a trigger frame foreliciting the uplink transmission from one or more STAs, receiving fromthe one or more STAs the uplink transmission according to a type of thetrigger frame, wherein when the uplink transmission is an uplink MUtransmission, each of at least one uplink frame includes a padding addedby a STA of a plurality of STAs such that transmissions from theplurality of STAs in the uplink MU transmission end at a same timeindicated by the trigger frame, and transmitting a frame in response tothe uplink MU transmission a predetermined time after an end of theuplink MU transmission.

In another aspect of the present disclosure, an STA apparatus fortransmitting an uplink frame to an AP in a wireless local area networkmay be provided. The STA apparatus may include a baseband processor, aRadio Frequency (RF) transceiver, a memory, etc. The baseband processormay be configured to receive from the AP a trigger frame for elicitingan uplink transmission from the STA using the transceiver, to transmitto the AP the uplink frame according to a type of the trigger frameusing the transceiver, wherein when the uplink frame is transmitted inan uplink MU transmission, the uplink frame includes a padding added bythe STA such that transmissions from a plurality of STAs including theSTA in the uplink MU transmission end at a same time indicated by thetrigger frame, and to receive from the AP a frame using the transceiverin response to the uplink MU transmission a predetermined time after anend of the uplink MU transmission.

In another aspect of the present disclosure, an AP apparatus forreceiving an uplink transmission in a wireless local area network may beprovided. The AP apparatus may include a baseband processor, an RFtransceiver, a memory, etc. The baseband processor may be configured totransmit a trigger frame for eliciting the uplink transmission from oneor more STAs using the transceiver, to receive from the one or more STAsthe uplink transmission according to a type of the trigger frame usingthe transceiver, wherein when the uplink transmission is an uplink MUtransmission, each of at least one uplink frame includes a padding addedby a STA of a plurality of STAs such that transmissions from theplurality of STAs in the uplink MU transmission end at a same timeindicated by the trigger frame, and to transmit a frame in response tothe uplink MU transmission using the transceiver a predetermined timeafter an end of the uplink MU transmission.

In another aspect of the present disclosure, a software orcomputer-readable medium having instructions executable for an STA totransmit an uplink frame to an AP in a wireless local area network maybe provided. The executable instructions may cause the STA to receivefrom the AP a trigger frame for eliciting an uplink transmission fromthe STA to transmit to the AP the uplink frame according to a type ofthe trigger frame, wherein when the uplink frame is transmitted in anuplink MU transmission, the uplink frame includes a padding added by theSTA such that transmissions from a plurality of STAs including the STAin the uplink MU transmission end at a same time indicated by thetrigger frame, and to receive from the AP a frame in response to theuplink MU transmission a predetermined time after an end of the uplinkMU transmission.

In another aspect of the present disclosure, a software orcomputer-readable medium having instructions executable for an AP toreceive an uplink transmission in a wireless local area network may beprovided. The executable instructions may cause the AP a memory, etc.The baseband processor may be configured to transmit a trigger frame foreliciting the uplink transmission from one or more STAs, to receive fromthe one or more STAs the uplink transmission according to a type of thetrigger frame, wherein when the uplink transmission is an uplink MUtransmission, each of at least one uplink frame includes a padding addedby a STA of a plurality of STAs such that transmissions from theplurality of STAs in the uplink MU transmission end at a same timeindicated by the trigger frame, and to transmit a frame in response tothe uplink MU transmission a predetermined time after an end of theuplink MU transmission.

It is to be understood that both the foregoing summarized features areexemplary aspects of the following detailed description of the presentdisclosure without limiting the scope of the present disclosure.

According to the present disclosure, a method and apparatus for uplinkchannel access in a HEW can be provided.

The advantages of the present disclosure are not limited to theforegoing descriptions, and additional advantages will become apparentto those having ordinary skill in the pertinent art to the presentdisclosure based upon the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a block diagram of a Wireless Local Area Network (WLAN)device;

FIG. 2 is a schematic block diagram of an exemplary transmitting signalprocessing unit in a WLAN;

FIG. 3 is a schematic block diagram of an exemplary receiving signalprocessing unit in a WLAN;

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs);

FIG. 5 is a conceptual diagram illustrating a procedure for transmittinga frame in Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) for avoiding collisions between frames in a channel;

FIG. 6 depicts an exemplary frame structure in a WLAN system;

FIG. 7 depicts an exemplary HE PPDU frame format;

FIG. 8 depicts an exemplary High Efficiency (HE) Physical layer ProtocolData Unit (PPDU) frame format according to the present disclosure;

FIG. 9 depicts subchannel allocation in a HE PPDU frame format accordingto the present disclosure;

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure;

FIG. 11 depicts the starting and ending points of an High EfficiencyLong Training Field (HE-LTF) field in a HE PPDU frame format accordingto the present disclosure;

FIG. 12 depicts a High Efficiency SIGnal B (HE-SIG-B) field and a HighEfficiency SIGnal C (HE-SIG-C) field in the HE PPDU frame formataccording to the present disclosure;

FIG. 13 depicts another example of a HE PPDU frame format according tothe present disclosure;

FIGS. 14 to 17 depict exemplary frame exchange sequences each includingUplink (UL) Multi-User (MU) transmission according to the presentdisclosure;

FIGS. 18 and 19 depict exemplary exchanges of a UL MU Poll Requestframe, a UL MU Poll Response frame, and a UL MU Poll Confirm frameaccording to the present disclosure;

FIG. 20 depicts UL MU random access of Stations (STAs) operating inpower save mode according to the present disclosure;

FIG. 21 depicts Access Category (AC)-based UL MU random access accordingto the present disclosure;

FIG. 22 depicts an exemplary trigger type-based UL transmission schemeaccording to the present disclosure;

FIG. 23 depicts an exemplary method according to the present disclosure;and

FIG. 24 depicts another exemplary method according to the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, only certain embodiments of thepresent disclosure have been shown and described, simply by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various different ways, all withoutdeparting from the spirit or scope of the present disclosure.Accordingly, the drawings and description are to be regarded asillustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

In a Wireless Local Area network (WLAN), a Basic Service Set (BSS)includes a plurality of WLAN devices. A WLAN device may include a MediumAccess Control (MAC) layer and a PHYsical (PHY) layer according toInstitute of Electrical and Electronics Engineers (IEEE) 802.11 seriesstandards. In the plurality of WLAN devices, at least one the WLANdevice may be an Access Point (AP) and the other WLAN devices may benon-AP Stations (non-AP STAs). Alternatively, all of the plurality ofWLAN devices may be non-AP STAs in an ad-hoc networking environment. Ingeneral, AP STA and non-AP STA may be each referred to as a STA or maybe collectively referred to as STAs. However, for ease of descriptionherein, only the non-AP STAs may be referred to herein as the STAs.

FIG. 1 is a block diagram of a WLAN device.

Referring to FIG. 1, a WLAN device 1 includes a baseband processor 10, aRadio Frequency (RF) transceiver 20, an antenna unit 30, a memory 40, aninput interface unit 50, an output interface unit 60, and a bus 70.

The baseband processor 10 may be simply referred to as a processor,performs baseband signal processing described in the presentspecification, and includes a MAC processor (or MAC entity) 11 and a PHYprocessor (or PHY entity) 15.

In an embodiment of the present disclosure, the MAC processor 11 mayinclude a MAC software processing unit 12 and a MAC hardware processingunit 13. The memory 40 may store software (hereinafter referred to as‘MAC software’) including at least some functions of the MAC layer. TheMAC software processing unit 12 may execute the MAC software toimplement some functions of the MAC layer, and the MAC hardwareprocessing unit 13 may implement the remaining functions of the MAClayer in hardware (hereinafter referred to as ‘MAC hardware’). However,the MAC processor 11 is not limited to the foregoing implementationexamples.

The PHY processor 15 includes a transmitting (TX) signal processing unit100 and a receiving (RX) signal processing unit 200.

The baseband processor 10, the memory 40, the input interface unit 50,and the output interface unit 60 may communicate with one another viathe bus 70.

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver22.

The memory 40 may further store an Operating System (OS) andapplications. The input interface unit 50 receives information from auser, and the output interface unit 60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When Multiple inputMultiple Output (MIMO) or Multi-User MIMO (MU-MIMO) is used, the antennaunit 30 may include a plurality of antennas.

FIG. 2 is a schematic block diagram of an exemplary transmission signalprocessor in a WLAN.

Referring to FIG. 2, the transmitting signal processing unit 100 mayinclude an encoder 110, an interleaver 120, a mapper 130, an InverseFourier Transformer (IFT) 140, and a Guard Interval (GI) inserter 150.

The encoder 110 encodes input data. For example, the encoder 110 may bea Forward Error Correction (FEC) encoder. The FEC encoder may include aBinary Convolutional Code (BCC) encoder followed by a puncturing device,or the FEC encoder may include a Low-Density Parity-Check (LDPC)encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before encoding to reduce theprobability of long sequences of 0s or 1s. If BCC encoding is used inthe encoder 110, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder 110,the transmitting signal processing unit 100 may not use the encoderparser.

The interleaver 120 interleaves the bits of each stream output from theencoder 110 to change the order of bits. Interleaving may be appliedonly when BCC encoding is used in the encoder 110. The mapper 130 mapsthe sequence of bits output from the interleaver 120 to constellationpoints. If LDPC encoding is used in the encoder 110, the mapper 130 mayfurther perform LDPC tone mapping in addition to constellation mapping.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may use a plurality of interleavers 120 and a plurality of mappers130 corresponding to the number of spatial streams, N_(SS). In thiscase, the transmitting signal processing unit 100 may further include astream parser for dividing outputs of the BCC encoders or output of theLDPC encoder into blocks that are sent to different interleavers 120 ormappers 130. The transmitting signal processing unit 100 may furtherinclude a Space-Time Block Code (STBC) encoder for spreading theconstellation points from the N_(SS) spatial streams into N_(STS)space-time streams and a spatial mapper for mapping the space-timestreams to transmit chains. The spatial mapper may use direct mapping,spatial expansion, or beamforming.

The IFT 140 converts a block of constellation points output from themapper 130 or the spatial mapper to a time-domain block (i.e., a symbol)by using Inverse Discrete Fourier Transform (IDFT) or Inverse FastFourier Transform (IFFT). If the STBC encoder and the spatial mapper areused, the IFT 140 may be provided for each transmit chain.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may insert Cyclic Shift Diversities (CSDs) to prevent unintentionalbeamforming. The CSD insertion may occur before or after IFT. The CSDmay be specified per transmit chain or may be specified per space-timestream. Alternatively, the CSD may be applied as a part of the spatialmapper.

When MU-MIMO is used, some blocks before the spatial mapper may beprovided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When MIMO or MU-MIMO is used, the GI inserter 150 and the RFtransmitter 21 may be provided for each transmit chain.

FIG. 3 is a schematic block diagram of an exemplary a receiving signalprocessor in a WLAN.

Referring to FIG. 3, the receiving signal processing unit 200 includes aGI remover 220, a Fourier Transformer (FT) 230, a demapper 240, adeinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into symbols. The GI remover 220 removes the GIfrom the symbol. When MIMO or MU-MIMO is used, the RF receiver 22 andthe GI remover 220 may be provided for each receive chain.

The FT 230 converts the symbol (i.e., the time-domain block) into ablock of constellation points by using a Discrete Fourier Transform(DFT) or a Fast Fourier Transform (FFT). The FT 230 may be provided foreach receive chain.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may include a spatial demapper for converting Fourier Transformedreceiver chains to constellation points of the space-time streams, andan STBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the FT 230or the STBC decoder to bit streams. If LDPC encoding is applied to thereceived signal, the demapper 240 may further perform LDPC tonedemapping before constellation demapping. The deinterleaver 250deinterleaves the bits of each stream output from the demapper 240.Deinterleaving may be applied only when a BCC encoding scheme is appliedto the received signal.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a plurality of demappers 240 and a plurality of deinterleavers250 corresponding to the number of spatial streams. In this case, thereceiving signal processing unit 200 may further include a streamdeparser for combining streams output from the deinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder 260, the receiving signal processing unit 200 may furtherinclude an encoder deparser for multiplexing the data decoded by aplurality of BCC decoders. If LDPC decoding is used in the decoder 260,the receiving signal processing unit 200 may not use the encoderdeparser.

In a WLAN system, Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) is a basic MAC access mechanism. The CSMA/CA mechanism isreferred to as Distributed Coordination Function (DCF) of IEEE 802.11MAC, shortly as a ‘listen before talk’ access mechanism. According tothe CSMA/CA mechanism, an AP and/or a STA may sense a medium or achannel for a predetermined time before starting transmission, that is,may perform Clear Channel Assessment (CCA). If the AP or the STAdetermines that the medium or channel is idle, it may start to transmita frame on the medium or channel. On the other hand, if the AP and/orthe STA determines that the medium or channel is occupied or busy, itmay set a delay period (e.g., a random backoff period), wait for thedelay period without starting transmission, and then attempt to transmita frame. By applying a random backoff period, a plurality of STAs areexpected to attempt frame transmission after waiting for different timeperiods, resulting in minimizing collisions.

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs).

WLAN devices may exchange data frames, control frames, and managementframes with each other.

A data frame is used for transmission of data forwarded to a higherlayer. The WLAN device transmits the data frame after performing backoffif a Distributed Coordination Function IFS (DIFS) has elapsed from atime when the medium has been idle. A management frame is used forexchanging management information which is not forwarded to the higherlayer. The WLAN device transmits the management frame after performingbackoff if an IFS such as the DIFS or a Point Coordination Function IFS(PIFS) has elapsed. Subtype frames of the management frame include abeacon frame, an association request/response frame, a proberequest/response frame, and an authentication request/response frame. Acontrol frame is used for controlling access to the medium. Subtypeframes of the control frame include a Request-To-Send (RTS) frame, aClear-To-Send (CTS) frame, and an ACKnowledgement (ACK) frame. In thecase that the control frame is not a response frame to another frame,the WLAN device transmits the control frame after performing backoff ifthe DIFS has elapsed. In case that the control frame is a response frameto another frame, the WLAN device transmits the control frame withoutperforming backoff if a Short IFS (SIFS) has elapsed. The type andsubtype of a frame may be identified by a type field and a subtype fieldin a Frame Control (FC) field.

On the other hand, a Quality of Service (QoS) STA transmits a frameafter performing backoff if an Arbitration IFS (AIFS) for an associatedAccess Category (AC), i.e., AIFS[i] (i is determined based on AC) haselapsed. In this case, the AIFC[i] may be used for a data frame, amanagement frame, or a control frame that is not a response frame.

In the example illustrated in FIG. 4, upon generation of a frame to betransmitted, a STA may transmit the frame immediately, if it determinesthat the medium is idle for the DIFS or AIFS[i] or longer. The medium isbusy for a time period during which the STA transmits the frame. Duringthe time period, upon generation of a frame to be transmitted, anotherSTA may defer access by confirming that the medium is busy. If themedium gets idle, the STA that intends to transmit the frame may performa backoff operation after a predetermined IFS in order to minimizecollision with any other STA. Specifically, the STA that intends totransmit the frame selects a random backoff count, waits for a slot timecorresponding to the selected random backoff count, and then attempttransmission. The random backoff count is determined based on aContention Window (CW) parameter and the medium is monitoredcontinuously during count-down of backoff slots (i.e. decrement abackoff count-down) according to the determined backoff count. If theSTA monitors the medium as busy, the STA discontinues the count-down andwaits, and then, if the medium gets idle, the STA resumes thecount-down. If the backoff slot count reaches 0, the STA may transmitthe next frame.

FIG. 5 is a conceptual diagram illustrating a CSMA/CA-based frametransmission procedure for avoiding collisions between frames in achannel.

Referring FIG. 5, a first STA (STA1) is a transmit WLAN device fortransmitting data, a second STA (STA2) is a receive WLAN device forreceiving the data from STA1, and a third STA (STA3) is a WLAN devicewhich may be located in an area where a frame transmitted from STA1and/or a frame transmitted from STA2 can be received by STA3.

STA1 may determine whether the channel is busy by carrier sensing. TheSTA1 may determine the channel occupation based on an energy level onthe channel or correlation of signals in the channel, or may determinethe channel occupation by using a Network Allocation Vector (NAV) timer.

After determining that the channel is not being used by other devicesduring DIFS (that is, the channel is idle), STA1 may transmit an RTSframe to STA2 after performing backoff. Upon receiving the RTS frame,STA2 may transmit a CTS frame as a response to the CTS frame after SIFS.

When STA3 receives the RTS frame, STA3 may set the NAV timer for atransmission duration of subsequently transmitted frame by usingduration information included in the RTS frame. For example, the NAVtimer may be set for a duration of SIFS+CTS frame duration+SIFS+dataframe duration+SIFS+ACK frame duration. When STA3 receives the CTSframe, it may set the NAV timer for a transmission duration ofsubsequently transmitted frames by using duration information includedin the CTS frame. For example, the NAV timer may be set for a durationof SIFS+a data frame duration+SIFS+an ACK frame duration. Upon receivinga new frame before the NAV timer expires, STA3 may update the NAV timerby using duration information included in the new frame. STA3 does notattempt to access the channel until the NAV timer expires.

When STA1 receives the CTS frame from STA2, it may transmit a data frameto STA2 after SIFS elapsed from the CTS frame has been completelyreceived. Upon successfully receiving the data frame, STA2 may transmitan ACK frame as a response to the data frame after SIFS elapsed.

When the NAV timer expires, STA3 may determine whether the channel isbusy through the use of carrier sensing. Upon determining that thechannel is not in use by other devices during DIFS and after the NAVtimer has expired, STA3 may attempt channel access after a contentionwindow after a random backoff has elapsed.

FIG. 6 depicts an exemplary frame structure in a WLAN system.

PHY layer may prepare a transmission MAC PDU (MPDU) in response to aninstruction (or a primitive, which is a set of instructions or a set ofparameters) by the MAC layer. For example, upon receipt of aninstruction requesting transmission start from the MAC layer, the PHYlayer may switch to a transmission mode, construct a frame withinformation (e.g., data) received from the MAC layer, and transmit theframe.

Upon detection of a valid preamble in a received frame, the PHY layermonitors a header of the preamble and transmits an instructionindicating reception start of the PHY layer to the MAC layer.

Information is transmitted and received in frames in the WLAN system.For this purpose, a Physical layer Protocol Data Unit (PPDU) frameformat is defined.

A PPDU frame may include a Short Training Field (STF) field, a LongTraining Field (LTF) field, a SIGNAL (SIG) field, and a Data field. Themost basic (e.g., a non-High Throughput (non-HT)) PPDU frame may includeonly a Legacy-STF (L-STF) field, a Legacy-LTF (L-LTF) field, a SIGfield, and a Data field. Additional (or other types of) STF, LTF, andSIG fields may be included between the SIG field and the Data fieldaccording to the type of a PPDU frame format (e.g., an HT-mixed formatPPDU, an HT-greenfield format PPDU, a Very High Throughput (VHT) PPDU,etc.).

The STF is used for signal detection, Automatic Gain Control (AGC),diversity selection, fine time synchronization, etc. The LTF field isused for channel estimation, frequency error estimation, etc. The STFand the LTF fields may be referred to as signals for OFDM PHY layersynchronization and channel estimation.

The SIG field may include a RATE field and a LENGTH field. The RATEfield may include information about a modulation scheme and coding rateof data. The LENGTH field may include information about the length ofthe data. The SIG field may further include parity bits, SIG TAIL bits,etc.

The Data field may include a SERVICE field, a Physical layer ServiceData Unit (PSDU), and PPDU TAIL bits. When needed, the Data field mayfurther include padding bits. A part of the bits of the SERVICE fieldmay be used for synchronization at a descrambler of a receiver. The PSDUcorresponds to a MAC PDU defined at the MAC layer and may include datagenerated/used in a higher layer. The PPDU TAIL bits may be used toreturn an encoder to a zero state. The padding bits may be used to matchthe length of the Data filed in predetermined units.

A MAC PDU is defined according to various MAC frame formats. A basic MACframe includes a MAC header, a frame body, and a Frame Check Sequence(FCS). The MAC frame includes a MAC PDU and may be transmitted andreceived in the PSDU of the data part in the PPDU frame format.

The MAC header includes a Frame Control field, a Duration/Identifier(ID) field, an Address field, etc. The Frame Control field may includecontrol information required for frame transmission/reception. TheDuration/ID field may be set to a time for transmitting the frame. Fordetails of Sequence Control, QoS Control, and HT Control subfields ofthe MAC header, refer to the IEEE 802.11-2012 technical specification.

The Frame Control field of the MAC header may include Protocol Version,Type, Subtype, To DS, From DS, More Fragment, Retry, Power Management,More Data, Protected Frame, and Order subfields. For the contents ofeach subfield in the Frame Control field, refer to the IEEE 802.11-2012technical specification.

A Null-Data Packet (NDP) frame format is a frame format that does notinclude a data packet. In other words, the NDP frame format includesonly a Physical Layer Convergence Protocol (PLCP) header part (i.e., theSTF, LTF, and SIG fields) of the general PPDU frame format, without theremaining part (i.e., the Data field) of the general PPDU frame format.The NDP frame format may be referred to as a short frame format.

The IEEE 802.11ax task group is discussing a WLAN system, called a HighEfficiency WLAN (HEW) system, that operates in 2.4 GHz or 5 GHz andsupports a channel bandwidth (or channel width) of 20 MHz, 40 MHz, 80MHz, or 160 MHz. The present disclosure defines a new PPDU frame formatfor the IEEE 802.11ax HEW system. The new PPDU frame format may supportMU-MIMO or OFDMA. A PPDU of the new format may be referred to as a ‘HEWPPDU’ or ‘HE PPDU’ (similarly, HEW xyz may be referred to as ‘HE xyz’ or‘HE-xyz’ in the following descriptions).

In present specification, the term ‘MU-MIMO or OFDMA mode’ includesMU-MIMO without using OFDMA, or OFDMA mode without using MU-MIMO in anorthogonal frequency resource, or OFDMA mode using MU-MIMO in anorthogonal frequency resource.

FIG. 7 depicts an exemplary HE PPDU frame format.

A transmitting STA may generate a PPDU frame according to the HE PPDUframe format as illustrated in FIG. 7 and transmit the PPDU frame to areceiving STA. The receiving STA may detect a PPDU and then process thePPDU.

The HE PPDU frame format may broadly include two parts: the first partincluding an L-STF field, an L-LTF field, an L-SIG field, an RL-SIGfield, a HE-SIG-A field, and a HE-SIG-B field and the second partincluding a HE-STF field, a HE-LTF field, and a HE-DATA field. 64-FFTbased on a channel bandwidth of 20 MHz may be applied to the first partand a basic subcarrier spacing of 312.5 kHz and a basic DFT period of3.2 μs may be included in the first part. 256-FFT based on a channelbandwidth of 20 MHz may be applied to the second part and a basicsubcarrier spacing of 75.125 kHz and a basic DFT period of 12.8 μs maybe included in the second part.

The HE-SIG-A field may include N_(HESIGA) symbols, the HE-SIG-B fieldmay include N_(HESIGB) symbols, the HE-LTF field may include N_(HELTF)symbols, and the HE-DATA field may include N_(DATA) symbols.

A detailed description of the fields included in the HE PPDU frameformat is given in Table 1.

TABLE 1 DFT Subcarrier Element definition duration period GI spacingDescription Legacy(L)- Non-high 8 μs — — equivalent to L-STF of anon-trigger-based STF throughput(HT) 1,250 kHz PPDU has a periodicity of0.8 μs Short Training with 10 periods. field L-LTF Non-HT Long 8 μs 3.2μs 1.6 μs 312.5 kHz Training field L-SIG Non-HT 4 μs 3.2 μs 0.8 μs 312.5kHz SIGNAL field RL-SIG Repeated Non- 4 μs 3.2 μs 0.8 μs 312.5 kHz HTSIGNAL field HE-SIG-A HE SIGNAL A N_(HESIGA) * 3.2 μs 0.8 μs 312.5 kHzHE-SIG-A is duplicated on each field 4 μs 20 MHz segment after thelegacy preamble to indicate common control information. N_(HESIGA) meansthe number of OFDM symbols of the HE-SIG-A field and is equal to 2 or 4.HE-SIG-B HE SIGNAL B N_(HESIGB) * 3.2 μs 0.8 μs 312.5 kHz N_(HESIGB)means the number of field 4 μs OFDM symbols of the HE-SIG-B field and isvariable. DL MU packet contains HE-SIG- B. SU packets and UL Triggerbased packets do not contain HE-SIG-B. HE-STF HE Short 4 or 8 μs — —non- HE-STF of a non-trigger-based Training field trigger- PPDU has aperiodicity of 0.8 μs based with 5 periods. A non-trigger-based PPDU:PPDU is not sent in response to a (equivalent trigger frame. to) 1,250The HE-STF of a trigger-based kHz; PPDU has a periodicity of 1.6 μstrigger- with 5 periods, A trigger-based based PPDU is an UL PPDU sentin PPDU: response to a trigger frame. (equivalent to) 625 kHz HE-LTF HELong N_(HELTF) * 2xLTF: supports 2xLTF: HE PPDU shall support 2xLTFTraining field (DTF 6.4 μs 0.8, 1.6, (equivalent mode and 4xLTF mode.period + 4xLTF: 3.2 μs to) 156.25 In the 2xLTF mode, HE-LTF GI) μs 12.8μs kHz; symbol excluding GI is equivalent 4xLTF: to modulating everyother tone in 78.125 kHz an OFDM symbol of 12.8 μs excluding GI, andthen removing the second half of the OFDM symbol in time domain,N_(HELTF) means the number of HE- LTF symbols and is equal to 1, 2, 4,6, 8. HE-DATA HE DATA N_(DATA) * 12.8 μs  supports 78.125 kHz  N_(DATA)means the number of HE field (DTF 0.8, 1.6, data symbols. period + 3.2μs GI) μs

L-STF is a non-HT Short Training field and may have a duration of 8 μsand a subcarrier spacing equivalent to 1250 kHz. L-STF of a PPDU whichis not based on a trigger may have a periodicity of 0.8 μs with 10periods. Herein, the trigger corresponds to scheduling information forUL transmission.

L-LTF is a non-HT Long Training field and may have a duration of 8 μs, aDFT period of 3.2 μs, a Guard Interval (GI) of 1.6 μs, and a subcarrierspacing of 312.5 kHz.

L-SIG is a non-HT SIGNAL field and may have a duration of 4 μs, a DFTperiod of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of 312.5 kHz.

RL-SIG is a Repeated Non-HT SIGNAL field and may have a duration of 4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz.

L-STF, L-LTF, L-SIG, and RL-SIG may be called legacy preambles.

HE-SIG-A is a HE SIGNAL A field and may have a duration of N_(HESIGA)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. HE-SIG-A may be duplicated on each 20 MHz segment after thelegacy preambles to indicate common control information. N_(HESIGA)represents the number of OFDM symbols of the HE-SIG-A field and may havea value of 2 or 4.

HE-SIG-B is a HE SIGNAL B field and may have a duration of N_(HESIGB)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. N_(HESIGB) represents the number of OFDM symbols of theHE-SIG-B field and may have a variable value. In addition, although a DLMulti-User (MU) packet may include the HE-SIG-B field, a Single-User(SU) packet and a UL trigger based packet may not include the HE-SIG-Bfield.

HE-STF is a HE Short Training field and may have a duration of 4 or 8μs. A non-trigger based PPDU may have a subcarrier spacing equivalent to1250 kHz and a trigger based PPDU may have a subcarrier spacingequivalent to 625 kHz. HE-STF of the non-triggered PPDU may have aperiodicity of 0.8 μs with 4 periods. The non-triggered PPDU is nottransmitted in response to a trigger field. HE-STF of the trigger basedPPDU may have a periodicity of 1.6 μs with 5 periods. The trigger basedPPDU is a UL PPDU transmitted in response to the trigger frame.

HE-LTF is a HE Long Training field and may have a duration ofN_(HELTF)*(DFT period+GI)μs. N_(HELTF) represents the number of HE-LTFsymbols and may have a value of 1, 2, 4, 6, or 8. A HE PPDU may supporta 2×LTF mode and a 4×LTF mode. In the 2×LTF mode, a HE-LTF symbol exceptfor a GI is equivalent to a symbol obtained by modulating every othertone in an OFDM symbol of 12.8 μs excluding a GI and then eliminatingthe first half or the second half of the OFDM symbol in the time domain.In the 4×LTF mode, a HE-LTF symbol excluding a GI are equivalent to asymbol obtained by modulating every fourth tone in an OFDM symbol of12.8 μs excluding a GI and then eliminating the first three-fourths orthe last three-fourths of the OFDM symbol in the time domain. 2×LTF mayhave a DFT period of 6.4 μs and 4×LTF may have a DFT period of 12.8 μs.A GI of HE-LTF may support 0.8 μs, 1.6 μs, and 3.2 μs. 2×LTF may have asubcarrier spacing equivalent to 156.25 kHz and 4×LTF may have asubcarrier spacing of 78.125 kHz.

HE-DATA is a HE DATA field and may have a duration of, N_(DATA)*(DFTperiod+GI)μs N_(DATA) represents the number of HE-DATA symbols. HE-DATAmay have a DFT period of 12.8 μs. A GI of HE-DATA may support 0.8 μs,1.6 μs, and 3.2 μs. HE-DATA may have a subcarrier spacing of 78.125 kHz.

The above description of the fields included in the HE PPDU frame formatmay be combined with exemplary HE PPDU frame formats described below.For example, characteristics of fields exemplarily described below maybe applied while a transmission order of the fields of the HE PPDU frameformat of FIG. 7 is maintained.

FIG. 8 depicts an exemplary HE PPDU frame format according to thepresent disclosure.

Referring to FIG. 8, the vertical axis represents frequency and thehorizontal axis represents time. It is assumed that frequency and timeincrease in the upward direction and the right direction, respectively.

In the example of FIG. 8, one channel includes four subchannels. AnL-STF, an L-LTF, an L-SIG, and an HE-SIG-A may be transmitted perchannel (e.g., 20 MHz), a HE-STF and a HE-LTF may be transmitted on eachsubchannel being a basic subchannel unit (e.g., 5 MHz), and a HE-SIG-Band a PSDU may be transmitted on each of subchannels allocated to a STA.A subchannel allocated to a STA may have a size required for PSDUtransmission to the STA. The size of the subchannel allocated to the STAmay be N (N=1, 2, 3, . . . ) times as large as the size of basicsubchannel unit (i.e., a subchannel having a minimum size). In theexample of FIG. 8, the size of a subchannel allocated to each STA isequal to the size of the basic subchannel unit. For example, a firstsubchannel may be allocated for PSDU transmission from an AP to STA1 andSTA2, a second subchannel may be allocated for PSDU transmission fromthe AP to STA3 and STA4, a third subchannel may be allocated for PSDUtransmission from the AP to STA5, and a fourth subchannel may beallocated for PSDU transmission from the AP to STA6.

While the term subchannel is used in the present disclosure, the termsubchannel may be referred to as Resource Unit (RU) or subband. Inparticular, the terms like OFDMA subchannel, OFDMA RU, OFDMA subband canbe used in embodiments for OFDMA in the present disclosure. Terms like abandwidth of a subchannel, a number of tones (or subcarriers) allocatedto a subchannel, a number of data tones (or data subcarriers) allocatedto a subchannel can be used to express a size of a subchannel. Asubchannel refers to a frequency band allocated to a STA and a basicsubchannel unit refers to a basic unit used to represent the size of asubchannel. While the size of the basic subchannel unit is 5 MHz in theabove example, this is purely exemplary. Thus, the basic subchannel unitmay have a size of 2.5 MHz.

In FIG. 8, a plurality of HE-LTF elements are distinguished in the timeand frequency domains. One HE-LTF element may correspond to one OFDMsymbol in time domain and one subchannel unit (i.e., a subchannelbandwidth allocated to a STA) in frequency domain. The HE-LTF elementsare logical units, and the PHY layer does not necessarily operate inunits of an HE-LTF element. In the following description, a HE-LTFelement may be referred to shortly as a HE-LTF.

A HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in time domain and in one channel unit (e.g., 20 MHz) infrequency domain.

A HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in time domain and in one subchannel unit (i.e., asubchannel bandwidth allocated to a STA) in frequency domain.

A HE-LTF field may be a set of HE-LTF elements, HE-LTF symbols, orHE-LTF sections for a plurality of stations.

The L-STF field is used for frequency offset estimation and phase offsetestimation, for preamble decoding at a legacy STA (i.e., a STA operatingin a system such as IEEE 802.11a/b/g/n/ac). The L-LTF field is used forchannel estimation, for the preamble decoding at the legacy STA. TheL-SIG field is used for the preamble decoding at the legacy STA andprovides a protection function for PPDU transmission of a third-partySTA (e.g., setting a NAV based on the value of a LENGTH field includedin the L-SIG field).

HE-SIG-A (or HEW SIG-A) represents High Efficiency Signal A (or HighEfficiency WLAN Signal A), and includes HE PPDU (or HEW PPDU) modulationparameters, etc. for HE preamble (or HEW preamble) decoding at a HE STA(or HEW STA). The parameters set included in the HEW SIG-A field mayinclude one or more of Very High Throughput (VHT) PPDU modulationparameters transmitted by IEEE 802.11ac stations, as listed in [Table 2]below, to ensure backward compatibility with legacy STAs (e.g., IEEE802.11 ac stations).

TABLE 2 Two parts of Number VHT-SIG-A Bit Field of bits DescriptionVHT-SIG-A1 B0-B1 BW 2 Set to 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz,and 3 for 160 MHz and 80 + 80 MHz B2 Reserved 1 Reserved. Set to 1. B3STBC 1 For a VHT SU PPDU:  Set to 1 if space time block coding is usedand set to 0  otherwise. For a VHT MU PPDU:  Set to 0. B4-B9 Group ID 6Set to the value of the TXVECTOR parameter GROUP_ID. A value of 0 or 63indicates a VHT SU PPDU; otherwise, indicates a VHT MU PPDU. B10-B21NSTS/Partial 12 For a VHT MU PPDU: NSTS is divided into 4 user AIDpositions of 3 bits each. User position p, where 0 ≤ p ≤ 3, uses bitsB(10 + 3p) to B(12 + 3p). The number of space- time streams for user uare indicated at user position p = USER_POSITION[u] where u = 0, 1, . .. , NUM_USERS − 1 and the notation A[b] denotes the value of array A atindex b. Zero space-time streams are indicated at positions not listedin the USER_POSITION array. Each user position is set as follows:  Setto 0 for 0 space-time streams  Set to 1 for 1 space-time stream  Set to2 for 2 space-time streams  Set to 3 for 3 space-time streams  Set to 4for 4 space-time streams Values 5-7 are reserved For a VHT SU PPDU:B10-B12  Set to 0 for 1 space-time stream  Set to 1 for 2 space-timestreams  Set to 2 for 3 space-time streams  Set to 3 for 4 space-timestreams  Set to 4 for 5 space-time streams  Set to 5 for 6 space-timestreams  Set to 6 for 7 space-time streams  Set to 7 for 8 space-timestreams B13-B21  Partial AID: Set to the value of the TXVECTOR parameter PARTIAL_AID. Partial AID provides an  abbreviated indicationof the intended recipient(s) of the  PSDU (see 9.17a). B22TXOP_PS_NOT_ALLOWED 1 Set to 0 by VHT AP if it allows non-AP VHT STAs inTXOP power save mode to enter Doze state during a TXOP. Set to 1otherwise. The bit is reserved and set to 1 in VHT PPDUs transmitted bya non-AP VHT STA. B23 Reserved 1 Set to 1 VHT-SIG-A2 B0 Short GI 1 Setto 0 if short guard interval is not used in the Data field.  Set to 1 ifshort guard interval is used in the Data field. B1 Short GI 1 Set to 1if short guard interval is used and N_(SYM) mod 10 = 9; N_(SYM)otherwise, set to 0. N_(SYM) is defined in 22.4.3. Disambiguation B2SU/MU[0] 1 For a VHT SU PPDU, B2 is set to 0 for BCC, 1 for LDPC CodingFor a VHT MU PPDU, if the MU[0] NSTS field is nonzero, then B2 indicatesthe coding used for user u with USER_POSITION[u] = 0; set to 0 for BCCand 1 for LDPC. If the MU[0] NSTS field is 0, then this field isreserved and set to 1. B3 LDPC Extra 1 Set to 1 if the LDPC PPDUencoding process (if an SU OFDM PPDU), or at least one LDPC user's PPDUencoding process Symbol (if a VHT MU PPDU), results in an extra OFDMsymbol (or symbols) as described in 22.3.10.5.4 and 22.3.10.5.5. Set to0 otherwise. B4-B7 SU VHT- 4 For a VHT SU PPDU: MCS/MU[1-3]  VHT-MCSindex Coding For a VHT MU PPDU:  If the MU[1] NSTS field is nonzero,then B4 indicates  coding for user u with USER_POSITION[u] = 1: set to 0 for BCC, 1 for LDPC. If the MU[1] NSTS field is 0, then  B4 is reservedand set to 1.  If the MU[2] NSTS field is nonzero, then B5 indicates coding for user u with USER_POSITION[u] = 2: set to 0  for BCC, 1 forLDPC. If the MU[2] NSTS field is 0, then  B5 is reserved and set to 1. If the MU[3] NSTS field is nonzero, then B6 indicates  coding for useru with USER_POSITION[u] = 3: set to 0  for BCC, 1 for LDPC. If the MU[3]NSTS field is 0, then  B6 is reserved and set to 1.  B7 is reserved andset to 1 B8 Beamformed 1 For a VHT SU PPDU:  Set to 1 if a Beamformingsteering matrix is applied to the  waveform in an SU transmission asdescribed in  20.3.11.11.2, set to 0 otherwise. For a VHT MU PPDU: Reserved and set to 1 NOTE - If equal to 1 smoothing is notrecommended. B9 Reserved 1 Reserved and set to 1 B10-B17 CRC 8 CRCcalculated as in 20.3.9.4.4 with c7 in B10. Bits 0-23 of HT-SIG1 andbits 0-9 of HT-SIG2 are replaced by bits 0-23 of VHT-SIG-A1 and bits 0-9of VHT-SIG-A2, respectively. B18-B23 Tail 6 Used to terminate thetrellis of the convolutional decoder. Set to 0.

[Table 2] illustrates fields, bit positions, numbers of bits, anddescriptions included in each of two parts, VHT-SIG-A1 and VHT-SIG-A2,of the VHT-SIG-A field defined by the IEEE 802.11ac standard. Forexample, a BW (BandWidth) field occupies two Least Significant Bits(LSBs), B0 and B1 of the VHT-SIG-A1 field and has a size of 2 bits. Ifthe 2 bits are set to 0, 1, 2, or 3, the BW field indicates 20 MHz, 40MHz, 80 MHz, or 160 and 80+80 MHz. For details of the fields included inthe VHT-SIG-A field, refer to the IEEE 802.11ac-2013 technicalspecification. In the HE PPDU frame format of the present disclosure,the HE-SIG-A field may include one or more of the fields included in theVHT-SIG-A field, and it may provide backward compatibility with IEEE802.11ac stations.

FIG. 9 depicts subchannel allocation in the HE PPDU frame formataccording to the present disclosure.

In FIG. 9, it is assumed that information indicating subchannelsallocated to STAs in HE PPDU indicates that 0 MHz subchannel isallocated to STA1 (i.e., no subchannel is allocated), a 5-MHz subchannelis allocated to each of STA2 and STA3, and a 10-MHz subchannel isallocated to STA4.

In the example of FIG. 9, an L-STF, an L-LTF, an L-SIG, and a HE-SIG-Amay be transmitted per channel (e.g., 20 MHz), a HE-STF and a HE-LTF maybe transmitted on each of subchannels being basic subchannel units(e.g., 5 MHz), and a HE-SIG-B and a PSDU may be transmitted on each ofsubchannels allocated to STAs. A subchannel allocated to a STA has asize required for PSDU transmission to the STA. The size of thesubchannel allocated to the STA may be an N (N=1, 2, 3, . . . ) multipleof the size of the basic subchannel unit (i.e., a minimum-sizesubchannel unit). In the example of FIG. 9, the size of a subchannelallocated to STA2 is equal to that of the basic subchannel unit, thesize of a subchannel allocated to STA3 is equal to that of the basicsubchannel unit, and the size of a subchannel allocated to STA4 is twicelarger than that of the basic subchannel unit.

FIG. 9 illustrates a plurality of HE-LTF elements and a plurality ofHE-LTF subelements which are distinguished in the time and frequencydomains. One HE-LTF element may correspond to one OFDM symbol in thetime domain and one subchannel unit (i.e., the bandwidth of a subchannelallocated to a STA) in the frequency domain. One HE-LTF subelement maycorrespond to one OFDM symbol in the time domain and one basicsubchannel unit (e.g. 5 MHz) in the frequency domain. In the example ofFIG. 9, one HE-LTF element includes one HE-LTF subelement in the 5-MHzsubchannel allocated to STA2 or STA3. On the other hand, one HE-LTFelement includes two HE-LTF subelements in the third subchannel, i.e.,10-MHz subchannel, allocated to STA4. A HE-LTF element and a HE-LTFsubelement are logical units and the PHY layer does not always operatein units of a HE-LTF element or HE-LTF subelement.

A HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in the time domain and one channel unit (e.g. 20 MHz) in thefrequency domain. That is, one HE-LTF symbol may be divided into HE-LTFelements by a subchannel width allocated to a STA and into HE-LTFsubelements by the width of the basic subchannel unit in the frequencydomain.

A HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in the time domain and one subchannel unit (i.e. thebandwidth of a subchannel allocated to a STA) in the frequency domain. AHE-LTF subsection may correspond to a set of HE-LTF elements in one ormore OFDM symbols in the time domain and one basic subchannel unit(e.g., 5 MHz) in the frequency domain. In the example of FIG. 9, oneHE-LTF section includes one HE-LTF subsection in the 5-MHz subchannelallocated to STA2 or STA3. On the other hand, one HE-LTF sectionincludes two HE-LTF subsections in the third subchannel, i.e., 10-MHzsubchannel, allocated to STA4.

A HE-LTF field may correspond to a set of HE-LTF elements (orsubelements), HE-LTF symbols, or HE-LTF sections (or subsections) for aplurality of stations.

For the afore-described HE PPDU transmission, subchannels allocated to aplurality of HE STAs may be contiguous in the frequency domain. In otherwords, for HE PPDU transmission, the subchannels allocated to the HESTAs may be sequential and any intermediate one of the subchannels ofone channel (e.g., 20 MHz) may not be allowed to be unallocated orempty. Referring to FIG. 8, if one channel includes four subchannels, itmay not be allowed to keep the third subchannel unallocated and empty,while the first, second, and fourth subchannels are allocated to STAs.However, the present disclosure does not exclude non-allocation of anintermediate subchannel of one channel to a STA.

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure.

In the example of FIG. 10, a plurality of contiguous channels (e.g.,20-MHz-bandwidth channels) and boundaries of the plurality of contiguouschannels are shown. In FIG. 10, a preamble may correspond to an L-STF,an L-LTF, an L-SIG, and a HE-SIG-A as illustrated in the examples ofFIGS. 8 and 9.

A subchannel for each HE STA may be allocated only within one channel,and may not be allocated with partially overlapping between a pluralityof channels. That is, if there are two contiguous 20-MHz channels CH1and CH2, subchannels for STAs paired for MU-MIMO-mode or OFDMA-modetransmission may be allocated either within CH1 or within CH2, and itmay be prohibited that one part of a subchannel exists in CH1 andanother part of the subchannel exists in CH2. This means that onesubchannel may not be allocated with crossing a channel boundary. Fromthe perspective of RUs supporting the MU-MIMO or OFDMA mode, a bandwidthof 20 MHz may be divided into one or more RUs, and a bandwidth of 40 MHzmay be divided into one or more RUs in each of two contiguous 20-MHzbandwidths, and no RU is allocated with crossing the boundary betweentwo contiguous 20-MHz bandwidths.

As described above, it is not allowed that one subchannel belongs to twoor more 20-MHz channels. Particularly, a 2.4-GHz OFDMA mode may supporta 20-MHz OFDMA mode and a 40-MHz OFDMA mode. In the 2.4-GHz OFDMA mode,it may not be allowed that one subchannel belongs to two or more 20-MHzchannels.

FIG. 10 is based on the assumption that subchannels each having the sizeof a basic subchannel unit (e.g., 5 MHz) in CH1 and CH2 are allocated toSTA1 to STA7, and subchannels each having double the size (e.g., 10 MHz)of the basic subchannel unit in CH4 and CH5 are allocated to STA8, STA9,and STA10.

As illustrated in the lower part of FIG. 9, although a subchannelallocated to STA1, STA2, STA3, STA5, STA6, or STA7 is fully overlappedonly with one channel (i.e., without crossing the channel boundary, orbelonging only to one channel), a subchannel allocated to STA4 ispartially overlapped with the two channels (i.e., crossing the channelboundary, or belonging to the two channels). In the forgoing example ofthe present disclosure, the subchannel allocation to STA4 is notallowed.

As illustrated in the upper part of FIG. 9, although a subchannelallocated to STA8 or STA10 is fully overlapped only with one channel(i.e., crossing the channel boundary, or belonging only to one channel),a subchannel allocated to STA9 is partially overlapped with two channels(i.e., crossing the channel boundary, or belonging to the two channels).In the forgoing example of the present disclosure, the subchannelallocation to STA9 is not allowed.

On the other hand, it may be allowed to allocate a subchannel partiallyoverlapped between a plurality of channels (i.e., crossing the channelboundary, or belonging to two channels). For example, in SU-MIMO modetransmission, a plurality of contiguous channels may be allocated to aSTA and any of one or more subchannels allocated to the STA may crossthe boundary between two contiguous channels.

While the following description is given with an assumption that onesubchannel has a channel bandwidth of 5 MHz in one channel having achannel bandwidth of 20 MHz, this is provided to simplify thedescription of the principle of the present disclosure and thus shouldnot be construed as limiting the present disclosure. For example, thebandwidths of a channel and a subchannel may be defined or allocated asvalues other than the above examples. In addition, a plurality ofsubchannels in one channel may have the same or different channelwidths.

FIG. 11 depicts the starting and ending points of a HE-LTF field in theHE PPDU frame format according to the present disclosure.

To support the MU-MIMO mode and the OFDMA mode, the HE PPDU frame formataccording to the present disclosure may include, in the HE-SIG-A field,information about the number of spatial streams to be transmitted to aHE STA allocated to each subchannel.

If MU-MIMO-mode or OFDMA-mode transmission is performed to a pluralityof HE STAs on one subchannel, the number of spatial streams to betransmitted to each of the HE STAs may be provided in the HE-SIG-A orHE-SIG-B field, which will be described later in detail.

FIG. 11 is based on the assumption that a first 5-MHz subchannel isallocated to STA1 and STA2 and two spatial streams are transmitted toeach STA in a DL MU-MIMO or OFDMA mode (i.e., a total of four spatialstreams are transmitted on one subchannel). For this purpose, a HE-STF,a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF, and a HE-SIG-B follow theHE-SIG-A field on the subchannel. The HE-STF is used for frequencyoffset estimation and phase offset estimation for the 5-MHz subchannel.The HE-LTFs are used for channel estimation for the 5-MHz subchannel.Since the subchannel carries four spatial streams, as many HE-LTFs(i.e., HE-LTF symbols or HE-LTF elements in a HE-LTF section) as thenumber of the spatial streams, that is, four HE-LTFs are required tosupport MU-MIMO transmission.

According to an example of the present disclosure, relationship betweena total number of spatial streams transmitted on one subchannel and anumber of HE-LTFs is listed in [Table 3].

TABLE 3 Total number of spatial streams transmitted on one subchannelNumber of HE-LTFs 1 1 2 2 3 4 4 4 5 6 6 6 7 8 8 8

Referring to [Table 3], if one spatial stream is transmitted on onesubchannel, at least one HE-LTF needs to be transmitted on thesubchannel. If an even number of spatial streams are transmitted on onesubchannel, at least as many HE-LTFs as the number of the spatialstreams need to be transmitted. If an odd number of spatial streamsgreater than one are transmitted on one subchannel, at least as manyHE-LTFs as a number of adding 1 to the number of the spatial streamsneed to be transmitted.

Referring to FIG. 11 again, it is assumed that the second 5-MHzsubchannel is allocated to STA3 and STA4 and one spatial streams per STAis transmitted in the DL MU-MIMO or OFDMA mode (i.e., a total of twospatial streams are transmitted on one subchannel). In this case, twoHE-LTFs need to be transmitted on the second subchannel, however, in theexample of FIG. 11, a HE-STF, a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF,and a HE-SIG-B follow the HE-SIG-A field on the subchannel (i.e., fourHE-LTFs are transmitted). This is for setting the same starting time ofPSDU transmission for subchannels allocated to other STAs paired withSTA3 and STA4 for MU-MIMO transmission. If only two HE-LTFs aretransmitted on the second subchannel, PSDUs are transmitted at differenttime points on the first and second subchannels. PSDU transmission oneach subchannel at a different time point results in discrepancy betweenOFDM symbol timings of subchannels, thereby no orthogonality ismaintained. To overcome this problem, an additional constraint need tobe imposed for HE-LTF transmission.

Basically, transmission of as many HE-LTFs as required is sufficient inan SU-MIMO or non-OFDMA mode. However, timing synchronization (oralignment) with fields transmitted on subchannels for other paired STAsis required in the MU-MIMO or OFDMA mode. Accordingly, the numbers ofHE-LTFs may be determined for all other subchannels based on asubchannel having the maximum number of streams in MU-MIMO-mode orOFDMA-mode transmission.

Specifically, the numbers of HE-LTFs may be determined for allsubchannels according to the maximum of the numbers of HE-LTFs (HE-LTFsymbols or HE-LTF elements in a HE-LTF section) required according tothe total numbers of spatial streams transmitted on each subchannel, fora set of HE STAs allocated to each subchannel. A “set of HE STAsallocated to each subchannel” is one HE STA in the SU-MIMO mode, and aset of HE STAs paired across a plurality of subchannels in the MU-MIMOmode. The ‘number of spatial streams transmitted on each subchannel’ isthe number of spatial streams transmitted to one HE STA in the SU-MIMOmode, and the number of spatial streams transmitted to a plurality of HESTAs paired on the subchannel in the MU-MIMO mode.

That is, it may be said that a HE-LTF field starts at the same timepoint and ends at the same time point in a HE PPDU for all users (i.e.HE STAs) in MU-MIMO-mode or OFDMA-mode transmission. Or it may be saidthat the lengths of HE-LTF sections are equal on a plurality ofsubchannels for all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-modetransmission. Or it may be said that the number of HE-LTF elementsincluded in each HE-LTF section is equal on a plurality of subchannelsfor all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-mode transmission.Accordingly, PSDU transmission timings may be synchronized among aplurality of subchannels for all HE STAs in MU-MIMO-mode or OFDMA-modetransmission.

As described above, the number of HE-LTF symbols (refer to FIG. 8) maybe 1, 2, 4, 6, or 8 in HE PPDU transmission in the MU-MIMO or OFDMAmode, determined according to the maximum of the numbers of spatialstreams on each of a plurality of subchannels. A different number ofspatial streams may be allocated to each of a plurality of subchannels,and the number of spatial streams allocated to one subchannel is thenumber of total spatial streams for all users allocated to thesubchannel. That is, the number of HE-LTF symbols may be determinedaccording to the number of spatial streams allocated to a subchannelhaving a maximum number of spatial streams by comparing the number oftotal spatial streams for all users allocated to one of a plurality ofsubchannels with the number of total spatial streams for all usersallocated to another subchannel.

Specifically, in HE PPDU transmission in the OFDMA mode, the number ofHE-LTF symbols may be 1, 2, 4, 6, or 8, determined based on the numberof spatial streams transmitted in a subchannel having a maximum numberof spatial streams across a plurality of subchannels. Further, in HEPPDU transmission in the OFDMA mode, the number of HE-LTF symbols may bedetermined based on whether the number of spatial streams transmitted ina subchannel having a maximum number of spatial streams across aplurality of subchannels is odd or even (refer to [Table 3]). That is,in HE PPDU transmission in the OFDMA mode, when the number (e.g., K) ofspatial streams transmitted in a subchannel having a maximum number ofspatial streams across a plurality of subchannels is an even number, thenumber of HE-LTF symbols may be equal to K. In HE PPDU transmission inthe OFDMA mode, when the number, K, of spatial streams transmitted in asubchannel having a maximum number of spatial streams across a pluralityof subchannels is an odd number greater than one, the number of HE-LTFsymbols may be equal to K+1.

When only one STA is allocated to one subchannel in OFDMA mode (i.e.,OFDMA mode without using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of spatial streams for a STA allocated to each subchannel.When more than one STA is allocated to one subchannel in OFDMA mode(i.e., OFDMA mode using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of STAs allocated to each subchannel and the number ofspatial streams for each STA allocated to each subchannel (e.g., if STA1and STA2 are allocated to one subchannel, sum of the number of spatialstreams for STA1 and the number of spatial streams for STA2).

When transmitting a HE PPDU frame in the MU-MIMO or OFDMA mode, atransmitter may generate P (P is an integer equal to or larger than 1)HE-LTF symbols (refer to FIG. 8) and transmit a HE PPDU frame includingat least the P HE-LTF symbols and a Data field to a receiver. The HEPPDU frame may be divided into Q subchannels in the frequency domain (Qis an integer equal to or larger than 2). Each of the P HE-LTF symbolsmay be divided into Q HE-LTF elements corresponding to the Q subchannelsin the frequency domain. That is, the HE PPDU may include P HE-LTFelements on one subchannel (herein, the P HE-LTF elements may belong toone HE-LTF section on the subchannel).

As described above, the number of HE-LTF elements (i.e., P) in one ofthe Q subchannels may be equal to the number of HE-LTF elements (i.e. P)of another subchannel. Also, the number of HE-LTF elements (i.e., P)included in a HE-LTF section in one of the Q subchannels may be equal tothe number of HE-LTF elements (i.e. P) included in a HE-LTF section inanother subchannel. The HE-LTF section of one of the Q subchannels maystart and end at the same time points as the HE-LTF section of anothersubchannel. Also, the HE-LTF sections may start and end at the same timepoints across the Q subchannels (i.e., across all users or stations).

Referring to FIG. 11 again, the third 5-MHz subchannel is allocated toSTA5 and one spatial stream is transmitted on the subchannel in SU-MIMO(considering all subchannels, a plurality of spatial streams aretransmitted to STA1 to STA6 in MU-MIMO or OFDMA mode). In this case,although transmission of one HE-LTF is sufficient for the subchannel, asmany HE-LTFs as the maximum of the numbers of HE-LTFs on the othersubchannels, that is, four HE-LTFs are transmitted on the subchannel inorder to align the starting points and ending points of the HE-LTFfields of the subchannels.

The fourth 5-MHz subchannel is allocated to STA6 and one spatial streamis transmitted on the subchannel in SU-MIMO (considering all othersubchannels, a plurality of spatial streams are transmitted to STA1 toSTA6 in MU-MIMO or OFDMA mode). In this case, although transmission ofone HE-LTF is sufficient for the subchannel, as many HE-LTFs as themaximum of the numbers of HE-LTFs on the other subchannels, that is,four HE-LTFs are transmitted on the subchannel in order to align thestarting points and ending points of the HE-LTF fields of thesubchannels.

In the example of FIG. 11, the remaining two HE-LTFs except two HE-LTFsrequired for channel estimation of STA3 and STA4 on the secondsubchannel, the remaining three HE-LTFs except one HE-LTF required forchannel estimation of STA5 on the third subchannel, and the remainingthree HE-LTFs except one HE-LTF required for channel estimation of STA6on the fourth subchannel may be said to be placeholders that areactually not used for channel estimation at the STAs.

FIG. 12 depicts a HE-SIG-B field and a HE-SIG-C field in the HE PPDUframe format according to the present disclosure.

To effectively support MU-MIMO-mode or OFDMA-mode transmission in the HEPPDU frame format according to the present disclosure, independentsignaling information may be transmitted on each subchannel.Specifically, a different number of spatial streams may be transmittedto each of a plurality of HE STAs that receive an MU-MIMO-mode orOFDMA-mode transmission simultaneously. Therefore, information about thenumber of spatial streams to be transmitted should be indicated to eachHE STA.

Information about the number of spatial streams on one channel may beincluded in, for example, a HE-SIG-A field. A HE-SIG-B field may includespatial stream allocation information about one subchannel. Also, aHE-SIG-C field may be transmitted after transmission of HE-LTFs,including Modulation and Coding Scheme (MCS) information about a PSDUand information about the length of the PSDU, etc.

With reference to the foregoing examples of the present disclosure,mainly the features of a HE PPDU frame structure applicable to a DLMU-MIMO-mode or OFDMA-mode transmission that an AP transmitssimultaneously to a plurality of STAs have been described. Now, adescription will be given of the features of a HE PPDU frame structureapplicable to a UL MU-MIMO-mode or OFDMA-mode transmission that aplurality of STAs transmits simultaneously to an AP.

The above-described various examples of structures of the HE PPDU frameformat supporting MU-MIMO-mode or OFDMA-mode transmission should not beunderstood as applicable only to DL without applicable UL. Rather, theexamples should be understood as also applicable to UL. For example, theabove-described exemplary HE PPDU frame formats may also be used for aUL HE PPDU transmission that a plurality of STAs simultaneouslytransmits to a single AP.

However, in the case of a DL MU-MIMO-mode or OFDMA-mode HE PPDUtransmission that an AP simultaneously transmits to a plurality of STAs,the transmission entity, AP has knowledge of the number of spatialstreams transmitted to a HE STA allocated to each of a plurality ofsubchannels. Therefore, the AP may include, in a HE-SIG-A field or aHE-SIG-B field, information about the total number of spatial streamstransmitted across a channel, a maximum number of spatial streams (i.e.,information being a basis of the number of HE-LTF elements (or thestarting point and ending point of a HE-LTF section) on eachsubchannel), and the number of spatial streams transmitted on eachsubchannel. In contrast, in the case of a UL MU-MIMO-mode or OFDMA-modeHE PPDU transmission that a plurality of STAs simultaneously transmitsto an AP, each STA being a transmission entity may be aware only of thenumber of spatial streams in a HE PSDU that it will transmit, withoutknowledge of the number of spatial streams in a HE PSDU transmitted byanother STA paired with the STA. Accordingly, the STA may determineneither the total number of spatial streams transmitted across a channelnor a maximum number of spatial streams.

To solve this problem, a common parameter (i.e., a parameter appliedcommonly to STAs) and an individual parameter (a separate parameterapplied to an individual STA) may be configured as follows in relationto a UL HE PPDU transmission.

For simultaneous UL HE PPDU transmissions from a plurality of STAs to anAP, a protocol may be designed in such a manner that the AP sets acommon parameter or individual parameters (common/individual parameters)for the STAs for the UL HE PPDU transmissions and each STA operatesaccording to the common/individual parameters. For example, the AP maytransmit a trigger frame (or polling frame) for a UL MU-MIMO-mode orOFDMA-mode transmission to a plurality of STAs. The trigger frame mayinclude a common parameter (e.g., the number of spatial streams across achannel or a maximum number of spatial streams) and individualparameters (e.g., the number of spatial streams allocated to eachsubchannel), for the UL MU-MIMO-mode or OFDMA-mode transmission. As aconsequence, a HE PPDU frame format applicable to a UL MU-MIMO or OFDMAmode may be configured without a modification to an exemplary HE PPDUframe format applied to a DL MU-MIMO or OFDMA mode. For example, eachSTA may configure a HE PPDU frame format by including information aboutthe number of spatial streams across a channel in a HE-SIG-A field,determining the number of HE-LTF elements (or the starting point andending point of a HE-LTE section) on each subchannel according to themaximum number of spatial streams, and including information about thenumber of spatial streams for the individual STA in a HE-SIG-B field.

Alternatively, if the STAs operate always according to thecommon/individual parameters received in the trigger frame from the AP,each STA does not need to indicate the common/individual parameters tothe AP during a HE PPDU transmission. Therefore, this information maynot be included in a HE PPDU. For example, each STA may have only todetermine the total number of spatial streams, the maximum number ofspatial streams, and the number of spatial streams allocated toindividual STA, as indicated by the AP, and configure a HE PPDUaccording to the determined numbers, without including information aboutthe total number of spatial streams or the number of spatial streamsallocated to the STA in the HE PPDU.

On the other hand, if the AP does not provide common/individualparameters in a trigger frame, for a UL MIMO-mode or OFDMA-mode HE PPDUtransmission, the following operation may be performed.

Common transmission parameters (e.g., channel BandWidth (BW)information, etc.) for simultaneously transmitted HE PSDUs may beincluded in HE-SIG-A field, but parameters that may be different forindividual STAs (e.g., the number of spatial streams, an MCS, andwhether STBC is used or not, for each individual STA) may not beincluded in HE-SIG-A field. Although the individual parameters may beincluded in HE-SIG-B field, information about the number of spatialstreams and information indicating whether STBC is used or not, need tobe transmitted before a HE-LTF field because the number of spatialstreams and the information indicating whether STBC is used or not aresignificant to determination of configuration information about apreamble and a PSDU in a HE PPDU frame format (e.g., the number ofHE-LTF elements is determined according to a combination of the numberof spatial streams and the information indicating whether STBC is usedor not). For this purpose, a HE PPDU frame format as illustrated in FIG.13 may be used for a UL HE PPDU transmission.

FIG. 13 depicts another exemplary HE PPDU frame format according to thepresent disclosure. The HE PPDU frame format illustrated in FIG. 13 ischaracterized in that a structure of HE-SIG-A, HE-SIG-B, and HE-SIG-Cfields similar to in FIG. 12 is used for a UL PPDU transmission.

As described before, if a UL MU-MIMO-mode or OFDMA-mode transmission isperformed by triggering of an AP (according to common/individualparameters provided by the AP), an individual STA may not need to reportan individual parameter to the AP. In this case, one or more of aHE-SIG-B field, a HE-SIG-C field, and a first HE-LTF element (i.e., aHE-LTF between a HE-STF field and a HE-SIG-B field) illustrated in FIG.13 may not exist. In this case, a description of each field given belowmay be applied only in the presence of the field.

In the example of FIG. 13, a HE-SIG-A field is transmitted per channel(i.e., per 20-MHz channel) and may include transmission parameterscommon to simultaneously transmitted HE PSDUs. Since the sameinformation is transmitted in up to HE-SIG-A fields in UL PPDUstransmitted by HE STAs allocated to subchannels, the AP may receive thesame signals from the plurality of STAs successfully.

A HE-SIG-B field is transmitted per subchannel in one channel. TheHE-SIG-B field may have an independent parameter value according to thetransmission characteristics of a HE PSDU transmitted on eachsubchannel. The HE-SIG-B field may include spatial stream allocationinformation and information indicating whether STBC is used or not, foreach subchannel. If MU-MIMO is applied to a subchannel (i.e., if aplurality of STAs perform transmission on a subchannel), the HE-SIG-Bfield may include a common parameter for the plurality of STAs paired onthe subchannel.

A HE-SIG-C field is transmitted on the same subchannel as the HE-SIG-Bfield and may include information about an MCS and a packet length. IfMU-MIMO is applied to a subchannel (i.e., if a plurality of STAs performtransmission on a subchannel), the HE-SIG-C field may include respectiveindividual parameters for each of the plurality of STAs paired on thesubchannel.

Similarly to DL MU-MIMO-mode or OFDMA-mode HE PPDU transmission,transmissions of PSDUs may start at different time points on subchannelsin UL MU-MIMO-mode or OFDMA-mode HE PPDU transmission, and if OFDMsymbols are not aligned accordingly, then the implementation complexityof an AP that receives a plurality of PSDUs increased. To solve thisproblem, ‘the number of HE-LTFs may be determined for all subchannelsaccording to the maximum of the numbers of HE LTFs required according tothe total numbers of spatial streams transmitted on each subchannel fora set of HE STAs allocated to each of subchannels’ as described withreference to the example of FIG. 11.

This feature may mean that the HE-LTF field start at the same time pointand end at the same time point across all users (i.e., HE STAs) in ULMU-MIMO-mode or OFDMA-mode transmission. Or it may be said that theHE-LTF sections of a plurality of subchannels have the same lengthacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission. Or itmay be said that each of the HE-LTF sections of a plurality ofsubchannels includes the same number of HE-LTF elements across all HESTAs in UL MU-MIMO-mode or OFDMA-mode transmission. Therefore, PSDUtransmission timings are synchronized between a plurality of subchannelsacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission.

As described before, a plurality of STAs may simultaneously transmitPSDUs in a HE PPDU frame format on their allocated subchannels or ontheir allocated spatial streams to an AP (i.e., referred to as ULMU-MIMO or OFDMA transmission or “UL MU transmission”) and maysimultaneously receive PSDUs in the HE PPDU frame format on theirallocated subchannels on their allocated spatial streams from the AP(i.e., referred to as DL MU-MIMO or OFDMA transmission or “DL MUtransmission”).

Now, a description will be given below of a UL MU transmission methodaccording to the present disclosure. For example, specific examples oftriggering for UL MU transmission, a transmission time of a UL MU PPDU,an ACK for UL MU transmission, error recovery for UL MU transmission,and UL MU triggering supporting random access for UL MU transmissionwill be described.

UL MU-MIMO transmission is taken as an example of UL MU transmission inthe following examples of the present disclosure. However, the examplesof the present disclosure is also applicable in the same manner to ULOFDMA transmission in which one transmission channel is divided into aplurality of subchannels and each STA performs simultaneous ULtransmission on an allocated subchannel. That is, UL MU transmissionincludes UL MU-MIMO transmission or UL OFDMA transmission in thefollowing description.

FIG. 14 depicts an exemplary frame exchange sequence including UL MUtransmission according to the present disclosure.

The AP may transmit a poll frame for UL MU transmission (i.e., a UL MUtrigger frame) to STAs to which UL MU transmission has been granted orrequested. To request UL MU transmission from STA1, STA2, STA3, andSTA4, the AP may transmit a UL MU Poll frame to STA1, STA2, STA3, andSTA4. The UL MU poll frame directed to the plurality of STAs may includeReceiver Address (i.e., an Address 1 field in a MAC header) set to abroadcast address, Transmitter Address (i.e., an Address 2 field in theMAC header) set to the MAC address of the AP, Basic Service SetIdentifier (BSSID), and payload with IDs (e.g., Association Identifiers(AIDs) of the STAs requested to perform the UL MU transmission. The ULMU Poll frame may further include information about a transmission time(length) of a UL MU PPDU to be transmitted simultaneously by the STAs.

Upon receipt of the UL MU Poll frame (i.e., a poll frame triggering ULMU transmission (UL MU-MIMO transmission or UL OFDMA transmission)), theSTAs may determine whether they are requested for the UL MU transmissionbased on information included in the UL MU Poll frame (e.g., UL MUtriggering information). If an STA determines that it is requested forthe UL MU transmission, the STA may transmit a UL MU PPDU to the APduring a given time period indicated by the information about thetransmission time of the UL MU PPDU (i.e., UL MU-MIMO PPDU or UL OFDMAPPDU), included in the UL MU Poll frame.

To align the transmission times of the UL MU PPDU simultaneouslytransmitted by the plurality of STAs, each of the STAs may include apadding in a UL MU PPDU that it transmits. That is, the STA maydetermine the transmission time of the UL MU PPDU (or the length of theUL MU PPDU) based on the information about a transmission time includedin the poll frame eliciting transmission of the UL MU PPDU, determinewhether to include a padding in the UL MU PPDU based on the determinedUL MU PPDU transmission time (or UL MU PPDU length), and determine thelength of the padding when the padding is to be included.

Specifically, since the plurality of STAs, which simultaneously transmitthe UL MU PPDU, may differ in data length, the STAs may include paddingsin the UL MU PPDU in order to prevent the increase of processingcomplexity of a UL MU PPDU receiver in case the UL transmissions end atdifferent time points in different resources (e.g., subchannels orstreams) allocated to the plurality of STAs, or to protect the UL MUPPDU from a third-party STA.

The padding may include a MAC padding or a PHY padding. The MAC paddingincludes adding as many padding bits as a required size after an MPDUincluding actual payload at the MAC layer. For example, an MPDU (i.e.,an A-MPDU subframe) of a predetermined size may be added after an MPDUincluding actual payload. The MPDU (i.e., the A-MPDU subframe) of thepredetermined size added for the MAC padding may correspond to one ormore 4-octet MPDUs (or A-MPDU subframes) having null data (e.g., azero-octet MSDU). The PHY padding is a padding used to match the numberof coded bits of the last OFDM symbol to a specific criterion (e.g., aparameter value for coded bits per OFDM symbol (i.e., N_(CBPS))), whenan A-MPDU is configured into one PSDU at the PHY layer. The number ofbits added as the padding may be 8 (i.e., 1 octet) or smaller.

In the example of FIG. 14, STA1 has data to be transmitted during atransmission time indicated by a poll frame triggering UL MUtransmission. Then, STA1 may transmit a UL MU PPDU with only a PHYpadding, without a MAC padding. In contrast, STA2, STA3, and STA4 do nothave data to be transmitted during the transmission time indicated bythe UL MU Poll frame. Then, each of STA2, STA3, and STA4 may determinethe length of a MAC padding based on the amount of data to betransmitted, apply the MAC padding, and then apply a PHY padding, thusperforming the UL MU PPDU transmission. Therefore, the transmissiontimes of the UL MU PPDU transmitted by STA1, STA2, STA3, and STA4 may bealigned with one another. That is, transmissions of all of the STAs mayend at a time point indicated by the UL MU Poll frame (or UL MU triggerframe) in the UL MU PPDU.

Further, in a UL MU PPDU in which transmissions of a plurality of STAshave the same transmission time (or end at the same time point), atransmission scheme of an ACK for the UL MU PPDU may be indicated by anACK Policy field included in the MAC header of data transmitted by theplurality of STAs. For example, if the ACK Policy is set to ImmediateBlock ACK, a data receiving STA may transmit a block ACK frameimmediately, for example, an SIFS after the UL MU PPDU transmissionends. Or in the case where the ACK Policy is set to Delayed Block ACK,if a data transmitting STA transmits a block ACK request frame to a datareceiving STA after data transmission ends, the data receiving STA maytransmit a frame including a block ACK in response to the block ACKrequest frame.

According to the present disclosure, one or more of STAs thatsimultaneously transmit data units may set the ACK Policies to ImmediateBlock ACK. If a plurality of STAs that simultaneously transmit dataunits set the ACK Policies commonly to Immediate Block ACK, the AP maysimultaneously transmit ACKs (e.g., a block ACK) in response to the dataunits simultaneously transmitted by the plurality of STAs. If the ACKPolicies of a first group including a part of the plurality of STAs thatsimultaneously transmit data units (e.g., an STA group including one ormore STAs) are set to Immediate Block ACK and the ACK Policies of asecond group (e.g., including the other STA(s) except for the STA(s) ofthe first group) are set to Delayed Block ACK, the AP may sequentiallytransmit an ACK(s) for the data unit(s) transmitted by the STA(s) of thesecond group after transmitting ACKs for a data unit(s) transmitted bythe STA(s) of the first group.

Upon receipt of UL MU transmission from the plurality of STAs, the APmay transmit ACK information for the received UL MU PPDU to theplurality of STAs. Information triggering UL MU transmission of theplurality of STAs may be transmitted along with the ACK information forthe plurality of STAs. For example, a block ACK frame may furtherinclude information triggering additional UL MU transmission or a pollframe triggering additional UL MU transmission may further include theACK information. That is, the AP may transmit the poll frame triggeringUL MU transmission and the block ACK frame in one PPDU.

FIG. 15 depicts another exemplary frame exchange sequence including ULMU transmission according to the present disclosure.

In the example of FIG. 15, it is assumed that STA1 fails to receive apoll frame triggering UL MU transmission from STA1, STA2, STA3, andSTA4. STA1 that has failed to receive the UL MU Poll frame may notparticipate in the UL MU transmission, whereas only STA2, STA3, and STA4may simultaneously transmit a UL MU PPDU.

In the UL MU transmission, STA2, STA3, and STA4 may apply MAC paddingsbased on a transmission time indicated by the UL MU Poll frame. Becausea MAC padding applied by each of STA2, STA3, and STA4 is based on thetransmission time of UL MU transmission including transmission of STA1,the MAC padding transmission periods of STA2, STA3, and STA4 do notinclude meaningful data transmission, unnecessarily occupying a wirelessmedium in UL MU transmission except for transmission of STA1. That is,if the other STAs apply MAC paddings to a UL MU PPDU in a situation inwhich a part (e.g., STA1) of a plurality of STAs has enough data to betransmitted during a transmission period given to the STAs by a UL MUPoll frame does not participate in UL MU transmission, systemperformance may be degraded.

FIG. 16 depicts another exemplary frame exchange sequence including ULMU transmission according to the present disclosure.

In the example of FIG. 16, it is assumed that STA1 fails to receive apoll frame triggering UL MU transmission of STA1, STA2, STA3, and STA4.STA1 that has failed to receive the UL MU Poll frame may not participatein the UL MU transmission, whereas only STA2, STA3, and STA4 maysimultaneously transmit a UL MU PPDU.

FIG. 16 illustrates an exemplary case in which a plurality of STAs areallowed to have different UL MU PPDU transmission times (or different ULMU PPDU lengths) in UL MU transmission of the STAs triggered by a UL MUPoll frame. That is, different transmission times of a UL MU PPDU for aplurality of STAs may mean that transmission times of legacy preambles(e.g., L-STFs, L-LTFs, and L-SIGs) and transmission times of HEpreambles (e.g., HE-SIG-As, HE-SIG-Bs, HE-STFs, HE-LTFs, etc.) arealigned among the plurality of STAs and data (e.g., PSDUs) starts at thesame time point but ends at different points for the plurality of STAsin the UL MU PPDU. Also, different transmission times of a UL MU PPDUfor a plurality of STAs may mean that the plurality of STAs do not applyMAC paddings. However, the plurality of STAs may apply PHY paddings fortransmission of the UL MU PPDU.

Further, if different UL MU PPDU transmission times are allowed for aplurality of STAs, even though a poll frame triggering UL MUtransmission includes information about a UL MU PPDU transmission time(or a UL MU PPDU length), the plurality of STAs may not apply MACpaddings based on the information about the UL MU PPDU transmissiontime. However, an STA(s) performing the UL MU transmission may performthe UL MU PPDU transmission within the UL MU PPDU transmission timeindicated by the UL MU Poll frame.

As described above, even though a part of a plurality of STAs whose ULMU transmission is triggered by a UL MU Poll frame do not perform the ULtransmission, if the other STA(s) does not apply a MAC padding totransmission of a UL MU PPDU, degradation of system performance causedby an unnecessary MAC padding may not occur.

In addition, in the case where a part of a plurality of STAs whose UL MUtransmission is triggered by a UL MU Poll frame do not perform the ULtransmission and the UL MU PPDU transmission time of the other STA(s) ischanged, if the ACK Policy of the other STA(s) is set to Immediate BlockACK, it may be ambiguous for the AP to determine an STA whose endingtime of a UL MU PPDU is a time when ACK information is to be transmittedin response to the UL MU PPDU. Moreover, since each of the plurality ofSTAs participating in the UL MU transmission does not have knowledge ofthe ending times of UL MU transmission of the other STAs except for theSTA, the STA does not determine when it will receive a frame includingACK information in response to the UL MU transmission. That is, if aplurality of different UL MU PPDU transmission times are allowed, eachof the plurality of STAs whose UL MU transmission is triggered may notexpect an immediate control response after transmitting the UL MU PPDUand may not define a timer and a timeout procedure for the controlresponse frame. Accordingly, if a plurality of different UL MU PPDUtransmission times are allowed, the ACK Policy of each of the pluralityof STAs may be set to Delayed Block ACK instead of Immediate Block ACK.

Now, a detailed description will be given of an operation fortransmitting a block ACK frame by an AP receiving a UL MU PPDU.

The AP may determine a transmission time of a block ACK frame to beafter an SIFS from, for example, the ending time of reception of thelast data unit of a UL MU PPDU (e.g., a time when the PHY layer invokesa PHY-RXEND.Indication primitive to the MAC layer), commonly in both thecases where the ACK Policies of data units from one or more of aplurality of STAs transmitting a UL MU PPDU are set to Immediate BlockACK as illustrated in FIGS. 14 and 15 and to Delayed Block ACK asillustrated in FIG. 16. However, the ending times of data units receivedfrom a plurality of STAs coincide with a time indicated by a UL MU Pollframe (or a UL MU trigger frame) in the case of FIGS. 14 and 15, whereasthe ending times of data units received from a plurality of STAs may bedifferent in the case of FIG. 16. In consideration of this aspect, theAP may determine the reception completion time of a UL MU PPDU.

In regard to this, an error recovery procedure for the UL MUtransmission triggering procedure will be described. When transmitting apoll frame triggering UL MU transmission, the AP may activate a UL MUpoll timer until the AP starts to receive a UL MU PPDU. The UL MU polltimer expires at a time point when a time period corresponding to a ULMU Poll timeout elapses. If the AP receives a valid start (e.g. a validPHY header) of a UL MU PPDU within a UL MU Poll timeout, the PHY of theAP may invoke the PHY-RXSTART.Indication primitive to the MAC.

If the PHY-RXSTART.Indication primitive is invoked within the UL MU Polltimeout, the AP may consider that at least one of STAs requested for theUL MU transmission has started to transmit a UL MU PPDU. That is, if theAP receives a data unit (e.g., an MPDU) from at least one STA indicatedby polling for UL MU transmission (or UL MU triggering), the AP maydetermine that it has started to receive the UL MU transmissionsuccessfully. That is, if the AP receives a data unit (e.g., an MPDU)from at least one STA indicated by polling for UL MU transmission (or ULMU triggering), the AP may determine that frame exchange initiated bythe UL MU polling (or UL MU triggering) is successful.

On the other hand, if the PHY-RXSTART.Indication primitive has not beeninvoked within the UL MU Poll timeout, the AP may perform the errorrecovery procedure, determining that an error has occurred to thepolling procedure for triggering UL MU transmission, which will bedescribed with reference to FIG. 17.

Meanwhile, when determining whether transmission of a UL MU PPDU hasbeen completed, the AP may invoke the PHY-RXEND.Indication primitive.The PHY-RXEND.Indication primitive corresponds to indication informationindicating to a local MAC entity that a current PSDU has been completelyreceived by the PHY. This primitive provides parameters as listed in[Table 4] below.

TABLE 4 PHY-RXEND.indication( RXERROR, RXVECTOR )

In [Table 4], an RXERROR parameter may deliver at least one of valuesindicating NoError, FormatVioloation, CarrierLost, and UnsupportedRate.After a receive state machine of the PHY detects what looks like a validpreamble and Start Frame Delimiter (SFD), a plurality of errorconditions may occur. The following parameters are returned for therespective error conditions.

-   -   NoError. This value is used to indicate that no error has        occurred during a reception process at the PHY.    -   Format Violation. This value is used to indicate that there is        an error in the format of a received PPDU.    -   CarrierLost. This value is used to indicate that a carrier        cannot be found during reception of an incoming PSDU and thus        PSDU processing cannot be performed any longer.    -   UnsupportedRate. This value is used to indicate that an        unsupported data rate has been detected during reception of an        incoming PPDU.    -   Filtered. This value is used to indicate that an incoming PPDU        has been filtered out due to a condition set by PHYCONFIG VECTOR        during reception of the incoming PPDU.

In [Table 4], RXVECTOR represents a list of parameters provided to thelocal MAC entity by the PHY, when the PHY receives a valid PHY header orthe last PSDU data bit of a received frame. Only if adot11RadioMeasurementActivated parameter is set to True, RXVECTOR isincluded. RXVECTOR may include all of MAC parameters and MAC managementparameters.

A PHY-RXEND.Indication primitive may be generated to indicate to thelocal MAC entity that the receive state machine of the PHY has completedreception with or without an error. In the presence of Signal Extension,the PHY-RXEND.Indication primitive may be generated at the ending pointof the Signal Extension.

If the value of RXERROR is NoERROR, the MAC may use thePHY-RXEND.Indication primitive as a reference for a channel accesstiming.

Upon receipt of a UL MU PPDU from a plurality of STAs, the AP maydetermine one reception starting time based on reception starting timesof the PPDU from the STAs and one reception ending time based onreception ending times of data units (e.g., PSDUs) from the STAs. Forthis purpose, the PHY of the AP may determine one reception startingtime or one reception ending time, or the MAC of the AP may determineone reception starting time or one reception ending time.

Specifically, upon receipt of a UL MU PPDU from a plurality of STAs, theAP may invoke one PHY-RXSTART.Indication primitive and onePHY-RXEND.Indication primitive from the PHY to the MAC. For example, thePHY may invoke the PHY-RXSTART.Indication primitive at one receptionstarting time (e.g., at one common reception starting time if the UL MUPPDU is received at the same starting time from the plurality of STAs asillustrated in the example of FIGS. 14 and 15, or at one (e.g., thelast) of different reception starting times of the UL MU PPDU from theplurality of STAs as illustrated in the example of FIG. 16) based ontime points at which data units start to be received from the pluralityof STAs. Also, the PHY may invoke the PHY-RXEND.Indication primitive atone reception ending time (e.g., at one common reception ending time ifthe UL MU PPDU reception is completed at the same time point from theplurality of STAs as illustrated in the example of FIGS. 14 and 15, orat one (e.g., the last) of different reception ending times of the UL MUPPDU from the plurality of STAs as illustrated in the example of FIG.16) based on time points at which the data units are completely receivedfrom the plurality of STAs.

Or the PHY of the AP may invoke individual PHY-RXSTART.Indicationprimitives and individual PHY-RXEND.Indication primitives to the MAC,for the UL MU PPDU received from the plurality of STAs. That is, the PHYmay invoke a plurality of PHY-RXSTART.Indication primitivescorresponding to the respective starting times of PPDU reception fromthe plurality of STAs to the MAC, and the MAC may determine one of them(e.g., one common reception starting time or the last reception startingtime) to be a PPDU reception starting time. Also, the PHY may invoke aplurality of PHY-RXEND.Indication primitives corresponding to therespective ending times of PPDU reception from the plurality of STAs tothe MAC, and the MAC may determine one of them (e.g., one commonreception ending time or the last reception ending time) to be a PPDUreception ending time.

If the AP has completely received PSDUS from all STAs transmitting theUL MU PPDU in this manner, the AP may determine a time point at whichthe PHY-RXEND.Indication is invoked to be an ending time of the UL MUPPDU reception. Accordingly, the AP may transmit a block ACK frame anSIFS after the ending time of the UL MU PPDU reception. For example, aPHY-RXEND.Indication primitive corresponding to one common ending timeof PSDU reception from a plurality of STAs may be invoked and a blockACK frame may be transmitted an SIFS after the invocation time of thePHY-RXEND.Indication primitive in the case of FIGS. 14 and 15. In thecase of FIG. 16, although PSDU reception from a plurality of STAs endsat different time points, a PHY-RXEND.Indication primitive correspondingto the last of the ending times may be invoked and a block ACK frame maybe transmitted an SIFS after the invocation time.

If the RXERROR parameter of a data unit received from at least one ofall STAs transmitting the UL MU PPDU is set to NoERROR, the AP maytransmit a block ACK frame to the STAs.

For example, upon receipt of a UL MU PPDU including data unitssimultaneously transmitted from STA1, STA2, STA3, and STA4, the AP mayconfirm that the ACK Policies of STA1, STA2, STA3, and STA4 areImmediate Block ACK and the PHY of the AP may transmit a block ACK framean SIFS after the ending time of the UL MU PPDU (e.g., a common timepoint at which the data units of STA1, STA2, STA3, and STA4 end) in theexample of FIG. 14. Herein, if the RXERROR parameter of at least one ofthe data units received from STA1, STA2, STA3, and STA4 is set toNoERROR, the AP may transmit a block ACK frame. For example, the blockACK frame may include ACK information for the data units received fromSTA1, STA2, STA3, and STA4.

In the example of FIG. 15, upon receipt of a UL MU PPDU including dataunits simultaneously transmitted from STA2, STA3, and STA4, the AP mayconfirm that the ACK Policies of STA2, STA3, and STA4 are ImmediateBlock ACK and transmit a block ACK frame an SIFS after the ending timeof reception of the UL MU PPDU at the PHY (e.g., a common ending time ofthe data units from STA2, STA3, and STA4). If the RXERROR parameter ofat least one of the data units transmitted from STA2, STA3, and STA4 isset to NoERROR, the AP may transmit the block ACK frame. For example,the block ACK frame may include ACK information for the data unitstransmitted from STA2, STA3, ad STA4. Or the block ACK frame may includeACK information for STA1 STA2, STA3, and STA4 requested for the UL MUtransmission (in this case, ACK information for STA1 may indicatefailure of data reception from STA1).

In the example of FIG. 16, upon receipt of a UL MU PPDU including dataunits simultaneously transmitted from STA2, STA3, and STA4, the AP mayconfirm that the ACK Policies of STA2, STA3, and STA4 are Delayed BlockACK and transmit a block ACK frame an SIFS after the ending time ofreception of the last UL MU PPDU at the PHY (e.g., a time at which aPHY-RXEND.Indication primitive is generated). If the RXERROR parameterof at least one of the data units transmitted from STA2, STA3, and STA4is set to NoERROR, the AP may transmit the block ACK frame. For example,the block ACK frame may include ACK information for the data unitstransmitted from STA2, STA3, ad STA4. Or the block ACK frame may includeACK information for STA1 STA2, STA3, and STA4 requested for the UL MUtransmission (in this case, ACK information for STA1 may indicatefailure of data reception from STA1).

Meanwhile, to protect a UL MU PPDU transmitted by a plurality of STAs(e.g., STA2, STA3, and STA4) in the example of FIG. 16, durationinformation included in the legacy preamble (e.g., an L-SIG field) ofthe UL MU PPDU may be set to a value (e.g., a time corresponding to anL-SIG Duration in FIG. 16) covering at least a remaining transmissiontime after transmission of the legacy preamble of the UL MU PPDU and atime at which a block ACK frame starts to be transmitted in response tothe UL MU PPDU (i.e., a time at which a valid PLCP header of the blockACK frame is transmitted). Thus, a third-party STA may check the legacypreamble of the UL MU PPDU and set a NAV so that a medium may beregarded as busy during a time period indicated by the L-SIG Duration.In the example of FIG. 16, the value of duration information of theL-SIG of STA2 transmitting the longest data unit may be largest and theNAV of the third-party STA may be set according to the value of theduration information of the L-SIG of STA2.

FIG. 17 depicts another exemplary frame exchange sequence including ULMU transmission according to the present disclosure.

FIG. 17 illustrates a procedure for recovering UL MU polling (or UL MUtriggering), when an AP transmits a UL MU Poll frame and aPHY-RXSTART.Indication primitive is not invoked during a UL MU Polltimeout. If the PHY-RXSTART.Indication primitive is not invoked duringthe UL MU Poll timeout period, the AP may determine whether a channel isidle during a specific IFS (referred to as an xIFS which may correspondto, for example, a PIFS or AIFS[i]) by CCA. If the channel is idle, theAP may transmit an additional UL MU Poll frame to STAs.

Hereinbelow, examples of UL MU triggering supporting random access forUL MU transmission according to the present disclosure will bedescribed.

Basically, UL MU transmission may be performed by UL MU polling (or ULMU triggering) of the AP. That is, STAs that will perform UL MUtransmission may be selected by a poll frame triggering the UL MUtransmission (or a UL MU trigger frame) provided by the AP, resourcesfor the UL MU transmission (e.g., a UL MU transmission time andsubchannels or streams used for the UL MU transmission) may beallocated, and the plurality of STAs may perform the UL MU transmissionbased on the allocated resources.

Meanwhile, random access for UL MU transmission means that STAsunspecified by an AP perform UL MU transmission or a plurality of STAsperform UL MU transmission using resources unspecified by the AP. An STAperforming the UL MU random access may be any of predetermined STAcandidates and the resources used for the UL MU random access may be anyof predetermined resource candidates. That is, the candidate STAs orcandidate resources for the UL MU random access may be predetermined andthe UL MU random access may be performed by any of the candidates STAsor using any of the candidate resources.

In an example of UL MU random access according to the presentdisclosure, a UL MU Poll Request frame and a UL MU Poll Response framemay be defined and used. The UL MU Poll Request frame may correspond toa frame triggering (or eliciting) UL MU random access of a plurality ofSTAs, and the UL MU Poll Response frame may correspond to a frametransmitted by each of the plurality of STAs by UL MU random access.Also, STAs that will participate in UL MU PPDU transmission (e.g., STAshaving data to be transmitted to an AP) may be predetermined throughexchange between a UL MU Poll Request frame and UL MU Poll Responseframes.

The examples of the present disclosure regarding a UL MU PPDUtransmission time provided by UL MU transmission triggering information,an ACK for UL MU transmission, and error recovery for UL MU transmissionas described before are applicable to a plurality of frames transmittedby UL MU random access. The description of a poll frame triggering UL MUtransmission in the foregoing examples is applicable to a frametriggering UL MU random access (e.g., a UL MU Poll Request frame), andthe description of UL MU transmission elicited by a poll frametriggering the UL MU transmission and an ACK transmitted in response tothe poll frame is applicable to a frame transmitted by UL MU randomaccess (e.g., a UL MU Poll Response frame) and an ACK (e.g., a UL MUPoll Confirm frame or a block ACK frame) transmitted in response to theframe.

To trigger UL MU random access, the AP may broadcast a UL MU PollRequest frame. That is, destination STAs are not specified for the UL MUPoll Request frame. Rather, any STA may receive the UL MU Poll Requestframe. Among STAs receiving the UL MU Poll Request frame, an STA havinga data frame to be transmitted to the AP (i.e., an STA to participate intransmission of a UL MU PPDU) may transmit a UL MU Poll Response frameto the AP. The UL MU Poll Response frame may be transmitted in immediateresponse to the UL MU Poll Request frame (i.e., the STA may transmit theUL MU Poll Response frame an SIFS after receiving the UL MU Poll Requestframe).

If a plurality of STAs transmit such UL MU Poll Response frames, the ULMU Poll Response frames may be configured in a UL MU PPDU format. Forexample, a UL MU Poll Response frame may have a fixed frame size and tominimize protocol overhead caused by collision, the UL MU Poll Responseframe may have a small frame size. For example, the UL MU Poll Responseframe may have a control frame format. Also, the UL MU Poll Responseframe may include identification information (e.g., a MAC address or anAID) of the transmitting STA (i.e., an STA to participate in the UL MUPPDU transmission), information about a buffer status, and informationabout resources to be used for the UL MU PPDU transmission (e.g. aresource unit, a subchannel, or the number of space-time streams).

FIGS. 18 and 19 depict exemplary exchanges of a UL MU Poll Requestframe, a UL MU Poll Response frame, and a UL MU Poll Confirm frameaccording to the present disclosure.

If the AP broadcasts a UL MU Poll Request frame, STAs that willparticipate in UL MU PPDU transmission may receive the UL MU PollRequest frame and transmit UL MU Poll Response frames to the AP an SIFSlater. In the examples of FIGS. 18 and 19, it is assumed that an AP iscapable of receiving a UL MU PPDU simultaneously from a plurality ofSTAs in four distinguished resources (e.g., four subchannels or fourspace-time streams). If one STA uses one resource, up to four STAs mayparticipate in the UL MU PPDU transmission.

As illustrated in the example of FIG. 18, if four STAs simultaneouslytransmit UL MU Poll Response frames, each STA using one resource (e.g.,one resource unit or one space-time stream), the AP may identify theSTAs that want to participate in UL MU PPDU transmission by receivingthe UL MU Poll Response frames from the four STAs. Thus, the AP maytransmit a UL MU Poll Confirm frame to STA1, STA2, STA3, and STA4 anSIFS after receiving the UL MU Poll Response frames. The UL MU PollConfirm frame may correspond to a poll frame triggering UL MUtransmission in the foregoing examples. Upon receipt of the UL MU PollConfirm frame, STA1, STA2, STA3, and STA4 may perform the UL MU PPDUtransmission based on trigger information provided by the AP. The ACKPolicy of a data unit from each of the plurality of STAs, included inthe UL MU PPDU may be set to Block ACK. Accordingly, the plurality ofSTAs may attempt to receive a block ACK frame from the AP an SIFS aftertransmitting the UL MU PPDU.

The example of FIG. 19 illustrates a case where more STAs than the APmay support for UL MU transmission respond to a UL MU Poll Requestframe. For example, if each STA uses one resource (e.g., one subchannelor one space-time stream), the AP may receive UL MU transmission fromfour STAs simultaneously in four distinguished resources. If five STAs(e.g., STA1, STA2, STA3, STA4, and STA5) out of the STAs receiving thebroadcast UL MU Poll Request frame transmit UL MU Poll Response frames,the AP may not receive the UL MU Poll Response frames successfully. Thatis, a plurality of STAs may perform UL MU random access according to aUL MU Poll Request frame. Transmissions of some STAs may collide duringrandom access. In this case, the AP may not successfully receive UL MUtransmission in the random access scheme. Therefore, the AP maybroadcast an additional UL MU Poll Request frame after a UL MU PollRequest timeout. If four STAs (e.g., STA1, STA2, STA3, and STA4)transmit UL MU Poll Response frames, the AP may receive the UL MU PollResponse frames successfully and then transmit a UL MU Poll Confirmframe to the four STAs. Therefore, the four STAs may perform UL MU PPDUtransmission and attempt to receive a block ACK frame.

Herein, a frame triggering simultaneous UL transmission (i.e., UL MUrandom access) of arbitrary STAs (e.g., a UL MU Poll Request frame) mayinclude response condition information. A response condition may includethe AC of UL data, a buffer size, etc. If the AP broadcasts a second ULMU Poll Request frame after a timeout occurs for a transmitted first ULMU Poll Request frame, a second response condition included in thesecond UL MU Poll Request frame may be reinforced or limited compared toa first response condition included in the first UL MU Poll Requestframe. For example, the number of STAs satisfying the second responsecondition may be set to be smaller than the number of STAs satisfyingthe first response condition. The example of FIG. 19 corresponds to acase in which although STA1, STA2, STA3, STA4, and STA5 satisfy thefirst response condition included in the first UL MU Poll Request frame,only STA1, STA2, STA3, and STA4 except for STA5 satisfy the secondresponse condition included in the second UL MU Poll Request frame.

Further, a frame triggering UL MU random access may include informationabout responding STA candidates or resource candidates as a responsecondition for the frame. STAs satisfying the response condition maytransmit response frames (e.g., UL MU Poll Response frames) by UL MUrandom access. If the AP fails to receive the response frames due tocollision between transmissions of the response frames, the AP maytransmit a frame triggering additional UL MU random access byreinforcing or limiting the response condition.

Also, a response frame transmitted in the UL MU random access scheme byan STA receiving the frame triggering UL MU random access may includeinformation about the buffer status of the responding STA, a property ofUL data (e.g., AC), or UL data.

FIG. 20 depicts UL MU random access of STAs operating in power save modeaccording to the present disclosure.

In the presence of data (i.e., DL data) buffered in the AP fortransmission to an STA operating in the power save mode, the STA maytransmit signaling information indicating that it has switched from adoze state to an awake state and requesting DL data (the signalinginformation may be included in a poll frame requesting DL data (e.g., aPower Save (PS)-Poll frame or a trigger frame triggering a serviceperiod, and this poll frame is distinguished from a poll frame ortrigger frame triggering UL MU transmission) to the AP based on aTraffic Indication Map (TIM) included in a beacon frame or the like. TheSTA operating in the power save mode may also operate in doze mode orawake mode to save power. Hereinbelow, an STA operating in the powersave mode is referred to as a TIM STA.

To support UL MU random access of a TIM STA, the AP may broadcast aframe triggering UL MU random access (e.g., a UL MU Poll Request frame)for TIM STAs. For example, a response condition included in the frametriggering UL MU random access may be set to limit responding STAcandidates to TIM STAs. Upon receipt of the frame triggering UL MUrandom access, an STA may transmit a PS-Poll frame or trigger framerequesting DL data to the AP in UL MU.

For example, the frame triggering UL MU random access of a plurality ofTIM STAs by the AP may correspond to a UL MU Poll Request frame, and thePS-Poll frames requesting DL data (or the trigger frame triggering aservice period) transmitted simultaneously by the plurality of STAs maycorrespond to UL MU Poll Response frames. To indicate that a UL MU PollResponse frame corresponds to a PS-Poll frame requesting DL data (or atrigger frame triggering a service period), an End of Service Period(EOSP) field of the UL MU Poll Response frame (e.g., the EOSP field maybe included in the QoS Control field of a MAC header) may be set to 0.That is, a UL MU Poll Response frame with an EOSP field set to 0 mayexecute the same function or play the same role as a PS-Poll framerequesting DL data by a TIM STA (or a trigger frame triggering a serviceperiod). Upon receipt of the UL MU Poll Response frame with the EOSPfield set to 0, the AP may transmit information indicating successfulreception of the UL MU Poll Response frames (i.e., PS-Poll framesrequesting DL data (or trigger frames triggering a service period) froma plurality of STAs to the STAs by transmitting a UL MU Poll Confirmframe or a block ACK frame to the plurality of TIM STAs.

In the example of FIG. 20, the AP may elicit transmissions of UL MU PollResponse frames (i.e., PS-Poll frames requesting DL data or triggerframes triggering a service period) from TIM STAs by random access bybroadcasting a UL MU Poll Request frame. For this purpose, signalinginformation indicating that a destination STA of the UL MU Poll Requestframe (or an STA allowed to respond to the UL MU Poll Request frame) isa TIM STA operating in the power save mode may be included in the UL MUPoll Request frame.

Among TIM STAs receiving the UL MU Poll Request frame, TIM STAsdetermining to request DL data (or to trigger a service period) maytransmit UL MU Poll Response frames each with an EOSP field set to 0 tothe AP an SIFS after receiving the UL MU Poll Request frame. In theexample of FIG. 20, STA1, STA2, STA3, and STA4 among a plurality of TIMSTAs determine to request DL data (or trigger a service period) andsimultaneously transmit UL MU Poll Response frames to the AP.

Upon receipt of the UL MU Poll Response frames each having an EOSP fieldset to 0 from STA1, STA2, STA3, and STA4, the AP may consider thereceived UL MU Poll Response frames to be PS-Poll frames requesting DLdata (or trigger frames triggering a service period) and transmit a ULMU Poll Confirm frame or a block ACK frame to STA1, STA2, STA3, and STA4in order to acknowledge reception of the UL MU Poll Response frames.

Upon confirmation of successful reception of the UL MU Poll Responseframes (i.e., the PS-Poll frames requesting DL data or the triggerframes triggering a service period) at the AP, the TIM STAs may be keptin the awake state to receive DL frames buffered in the AP. While theTIM STAs are in the awake state, the AP may simultaneously transmit a DLMU PPDU (i.e., a DL MU-MIMO PPDU or a DL OFDMA PPDU) including the DLdata buffered for the plurality of TIM STAs in the AP to the pluralityof TIM STAs.

Meanwhile, upon receipt of a frame with an EOSP field set to 1 from theAP, a TIM STA may switch from the awake state to the doze state.

In this manner, the TIM STAs' request of UL data or triggering of aservice period by UL MU random access may be supported by exchanging aframe triggering UL MU random access of the TIM STAs (e.g., a UL MU PollRequest frame), UL MU random access-based response frames (e.g., UL MUPoll Response frames) of the TIM STAs, and an ACK for the UL MU randomaccess of the TIM STAs (e.g., a UL MU Poll Confirm frame or a block ACKframe). Herein, because the UL MU Poll Confirm frame or the block ACKframe does not include information triggering UL MU PPDU transmission ofthe plurality of TIM STAs, the TIM STAs may not perform the UL MU PPDUtransmission in response to the UL MU Poll Confirm frame or the blockACK frame.

FIG. 21 depicts AC-based UL MU random access according to the presentdisclosure.

To acquire a TXOP for starting a UL MU transmission procedure, the APmay perform a backoff procedure. For example, after determining that achannel is idle by sensing the channel during a PIFS, DISF, or AIFS[i],the AP may select a random backoff count, wait during a slot timecorresponding to the random backoff count, and attempt to transmit aframe. The random backoff count may be selected from a range of 0 to CWwhere CW is a contention window parameter value. Once the random backoffprocedure starts, the AP activates a backoff timer according to thedetermined backoff count. If the channel is idle during a slot time(e.g., aSlotTime), the AP may decrement the backoff count by 1 eachtime. If the channel is monitored as busy, the AP discontinues thecount-down and waits. If the medium is idle, the AP resumes theremaining count-down. If the backoff timer reaches 0, the AP maytransmit a frame (e.g., a poll frame triggering UL MU transmission or aUL MU Poll Request frame).

An AIFS may be determined according to the AC of the backoff procedure.The AC may be determined to be one of AC_VO (Access Category Voice),AC_VI (Access Category Video), AC_BE (Access Category Best Effort), andAC_BK (Access Category Back Ground).

In the present disclosure, the AC of a backoff procedure fortransmission of a UL MU Poll Request frame is a primary AC. A frametriggering UL MU random access (e.g., a UL MU Poll Request frame) mayinclude primary AC information (or a primary AC field) as responsecondition information. Accordingly, STAs having traffic corresponding toan AC indicated by the primary AC information included in the frametriggering UL MU random access (e.g., the UL MU Poll Request frame)among a plurality of STAs may transmit UL MU random access-basedresponse frames (e.g., UL MU Poll Response frames). That is, it may besaid that UL MU random access is triggered by the frame triggering ULrandom access for the STAs having traffic corresponding to the ACindicated by the primary AC information among any STAs. Further, the ULMU random access-based response frames (e.g., the UL MU Poll Responseframes) may include information indicating the AC of the STAsparticipating in the UL MU random access (i.e., primary AC information).Therefore, the AP may determine whether the STAs having trafficcorresponding to the primary AC set when the UL MU random access wastriggered has performed UL MU random access and may determine STAs whoseUL MU transmission is to be triggered.

A frame triggering UL MU transmission (e.g., a UL MU Poll Confirm frame)may include primary AC information. Accordingly, STAs having trafficcorresponding to an AC indicated by the primary AC information includedin the frame triggering UL MU transmission (e.g., the UL MU Poll Confirmframe) may perform the UL MU transmission. That is, it may be said thatUL MU transmission is indicated to STAs having traffic corresponding tothe AC indicated by the primary AC information by the frame triggeringUL MU transmission. Further, the UL MU transmission (e.g., UL MU PPDUtransmission) may include information indicating the AC of traffictransmitted in UL MU.

In the example of FIG. 21, it is assumed that an AC (i.e., a primary AC)used for the AP to transmit a UL MU Poll Request frame is AC_VO. Inother words, the primacy AC information of the UL MU Poll Request framemay be set to a value corresponding to AC_VO. Among STAs receiving theUL MU Poll Request frame, only STAs having traffic corresponding toAC_VO indicated by the primary AC information (e.g., STA1, STA2, STA3,and STA4) may transmit UL MU Poll Response frames to the AP by UL MUrandom access. Primary AC information included in the UL MU PollResponse frames may also be set to a value indicating AC_VO. Therefore,the AP may request or indicate STA1, STA2, STA3, and STA4 to transmittraffic corresponding to AC_VO by transmitting a UL MU Poll Confirmframe triggering UL MU transmission of STA1, STA2, STA3, and STA4.Primary AC information included in the UL MU Poll Confirm frame may alsobe set to a value indicating AC_VO. Therefore, traffic transmitted in aUL MU PPDU elicited by the UL MU Poll Confirm frame by each STA may beconfined to traffic corresponding to AC_VO.

Additionally, UL MU transmission efficiency may be increased by notlimiting UL MU random access or UL MU transmission to a specific AC. Forexample, if primary AC information included in a UL MU Poll Requestframe, a UL MU Poll Response frame, and a UL MU Poll Confirm frame isset to a specific value other than the values indicating AC_VO, AC_VI,AC_BE, and AC_BK, it may be considered that there is no constraint on anAC for UL MU random access or UL MU transmission (i.e., UL MU randomaccess or UL MU transmission is allowed for traffic corresponding to anyAC).

If the primary AC information of a UL MU Poll Request frame is set to aspecific value other than the values indicating AC_VO, AC_VI, AC_BE, andAC_BK, STAs having traffic to be transmitted to the AP may transmit ULMU Poll Response frames irrespective of the ACs of the traffic. Inaddition, if the primary AC information of a UL MU Poll Confirm frame isset to a specific value other than the values indicating AC_VO, AC_VI,AC_BE, and AC_BK, STAs whose UL MU transmission is triggered by the ULMU Poll Confirm frame may transmit traffic having any ACs in a UL MUPPDU to the AP.

Further, UL MU transmission efficiency may be increased by enabling STAswhose UL MU transmission is triggered to determine whether to performthe UL MU transmission before starting to transmit a UL MU PPDU. Forexample, STAs receiving a UL MU Poll Confirm frame may perform virtualcarrier sensing (e.g., NAV check). Only when a channel is idle, the STAsmay transmit the UL MU PPDU. On the contrary, if a virtual sensingresult of an STA receiving the UL MU Poll Confirm frame indicates achannel idle state, the STA may not participate in transmission of theUL MU PPDU. This is because even though a carrier sensing result of theAP indicates a channel idle state, carrier sensing results of STAs forwhich UL MU transmission is triggered by the AP may not indicate thechannel idle state. If an STA performs UL MU transmission even though acarrier sensing result of the STA indicates a channel busy state, thetransmission of the STA may collide with transmission of another STAcurrently occupying the channel. Therefore, only when a virtual carriersensing result of each of STAs receiving a frame triggering UL MUtransmission (e.g., a UL MU Poll Confirm frame) indicates a channel idlestate (e.g., a NAV value is not a non-zero value), the STA may determinethat it can perform the UL MU transmission.

Now, a description will be given of a method for indicating ordetermining a different UL transmission scheme according to informationincluded in a trigger in trigger-based UL transmission.

UL transmission schemes may be classified into UL SU transmission inwhich one STA transmits a frame to an AP during a specific time period,and UL MU transmission in which a plurality of STAs simultaneouslytransmit frames to an AP during a specific time period, according to thenumber of users participating in UL transmission. UL transmissionschemes may also be classified into control frame transmission (e.g.,transmission of a CTS frame, an ACK frame, or a PS-Poll frame), dataframe transmission, and management frame transmission (e.g.,transmission of an Association Response frame, a Reassociation Responseframe, or a Probe Response frame), according to the type of atransmitted MAC frame.

According to the present disclosure, a UL transmission scheme may bedetermined according to the type of a trigger in trigger-based ULtransmission. For example, a first-type trigger frame may elicit a UL MUcontrol frame (e.g., MU CTS), a second-type trigger frame may elicit aUL SU control frame (e.g., SU CTS), a third-type trigger frame mayelicit UL MU transmission (e.g., transmission of UL MU data frames), anda fourth-type trigger frame may elicit UL MU random transmission.

More specifically, the type of a response frame may be determinedaccording to a version of the response frame requested by a triggerframe, the number of STAs to participate in transmission of the responseframe, and whether an STA to participate in transmission of the responseframe is specified, in trigger-based UL transmission.

For example, different types of response frames may be transmitted for afirst version and a second version as versions of a response framerequested by a trigger frame. Specifically, the first version may be anolder version than the second version. More specifically, afirst-version response frame may be a response frame conforming to alegacy PPDU format (e.g., a PPDU format defined by the IEEE 802.11a/b/g/n/ac standard, for example, a non-HT PPDU format), and asecond-version response frame may be a response frame conforming to theafore-described HE PPDU format.

Further, if the trigger frame requests a first-version response frame, adifferent type of response frame may be transmitted depending on whetherthe trigger frame indicates one STA or one or more STAs. If the triggerframe indicates a first-version response frame from one STA, theindicated one STA may transmit a first-version UL response frame (e.g.,a UL SU control frame, specifically a legacy CTS (or SU CTS) frame). Onthe other hand, if the trigger frame indicates first-version responseframes from one or more STAs, the indicated one or more STAs maysimultaneously transmit first-version UL response frames (e.g., UL MUcontrol frames, specifically MU CTS frames) simultaneously. That is, atrigger frame eliciting transmission of first-version UL response framesfrom one or more STAs is referred to as a first-type trigger frame, anda trigger frame eliciting transmission of a first-version UL responseframe from one STA is referred to as a second-type trigger frame. Forexample, the first-type trigger frame may correspond to a UL MU PollConfirm frame, and first-version UL response frames that a plurality ofSTAs transmit simultaneously in response to the first-type trigger framemay correspond to legacy CTS frames. The second-type trigger frame maycorrespond to a frame requesting transmission of a CTS frame from oneSTA and a first-version UL response frame transmitted in response to thesecond-type trigger frame by the one STA may correspond to a legacy CTSframe.

Meanwhile, if the trigger frame requests a second-version responseframe, a different type of response frame may be transmitted dependingon whether the trigger frame indicates one or more STAs (e.g. whetherthe trigger frame implicitly or explicitly indicates resources for oneor more STAs) or whether the trigger frame indicates no STA (e.g.,whether the trigger frame does not indicate resources for one or moreSTAs). If the trigger frame indicates second-version response framesfrom one or more STAs, the indicated one or more STAs may participate inUL MU transmission (e.g., transmission of UL MU data frames) usingresources indicated by the trigger frame. If the trigger frame indicatesa second-version response frame without indicating any STA, one or moreSTAs receiving this trigger frame may participate in UL MU transmissionusing resources for random access (i.e., resources allowing collisionbetween transmissions of the one or more STAs). That is, a trigger frameeliciting transmission of second-version UL response frames from one ormore STAs is referred to as a third-type trigger frame, and a triggerframe eliciting random access-based transmission of second-version ULresponse frames from one or more STAs is referred to as a fourth-typetrigger frame. For example, the third-type trigger frame may correspondto a UL MU Poll Confirm frame, and second-version UL response framestransmitted simultaneously in response to the third-type trigger frameby a plurality of STAs may correspond to a UL MU PPDU frame. Thefourth-type trigger frame may correspond to a UL MU Poll Request framerequesting random access of any STA, and a second-version UL responseframe transmitted in response to the UL MU Poll Request frame by the STAmay correspond to a UL MU Poll Response frame.

For example, STAs which have received a poll frame triggering UL MUtransmission (e.g., a UL MU Poll Confirm frame) may provide NAVinformation around them in order to protect a channel for transmissionof a UL MU PPDU from a third-party STA (e.g., an STA of an OverlappingBSS (OBSS), a legacy STA, etc.) that does not listen to the UL MU PPDU.For this purpose, the STAs may transmit CTS frames. These CTS frames maybe transmitted in a legacy PPDU (e.g., a NON-HT PPDU or a NON-HTduplicate PPDU) so that all third-party STAs may receive the CTS frames.In this manner, UL MU transmission efficiency can be increased in anOBSS environment by allowing adjacent OBSS STAs to set a NAV value usinga trigger-based CTS frame.

If a plurality of STAs transmit CTS frames simultaneously based on atrigger, these CTS frames may correspond to MU CTS frames, and a triggerframe triggering the MU CTS frames may correspond to as an MU RTS frame.If one STA transmits a CTS frame based on a trigger, this CTS frame maycorrespond to an SU CTS frame and a trigger frame eliciting an SU CTSframe may correspond to an SU RTS frame.

In addition, CTS frames that STAs transmit in response to a poll frametriggering UL MU transmission (e.g., a UL MU Poll Confirm frame) may beCTS-to-Self frames (i.e., CTS frames each including an RA set to the MACaddress of an STA itself).

To allow third-party STAs to successfully receive CTS framescorresponding to legacy PPDUs transmitted simultaneously by a pluralityof STAs, MPDUs (i.e., CTS frames) included in PSDUs transmitted by theplurality of STAs may carry the same contents. For example, the samescrambling sequence used for PSDU encoding may be set for all of theplurality of CTS frames. Further, to include the same information in theplurality of CTS frames, the RA fields of the CTS frames may be set tothe same value (e.g., the BSSID of the AP), unlike CTS-to-Self frames.In addition, the Frame Control fields, the Duration fields, etc. of theCTS frames may be set to the same values.

FIG. 22 depicts an exemplary trigger type-based UL transmission schemeaccording to the present disclosure.

In the example of FIG. 22, the AP may transmit a UL MU Poll Requestframe through a random backoff procedure. Among STAs receiving the UL MUPoll Request frame, a plurality of STAs (e.g., STA1, STA2, STA3, andSTA4) having traffic corresponding to AC_VO indicated by primary ACinformation may transmit UL MU Poll Response frames to the AP. Uponreceipt of the UL MU Poll Response frames from the plurality of STAs,the AP may request or indicate UL MU transmission to STA1, STA2, STA3,and STA4 by a UL MU Poll Confirm frame.

If the UL MU Poll Confirm frame is a first type (e.g., MU RTS), STA1,STA2, STA3, and STA4 may configure and transmit CTS frames (e.g.,CTS-to-Self frames) in a legacy PPDU format before starting to transmita UL MU PPDU. In this manner, the plurality of STAs may transmit a UL MUPPDU including traffic corresponding to AC_VO an SIFS after transmittingthe MU CTS frames simultaneously.

As illustrated in FIG. 22, the transmission times (or lengths) of aplurality of CTS frames may be set to the same value. For this purpose,the seed value of the scrambling sequence, MCS, or rate of a triggerframe (e.g., a UL MU Poll Confirm frame or an MU RTS frame) triggeringthe plurality of CTS frames that are transmitted simultaneously may beused commonly for transmission of the plurality of CTS frames.

Additionally, transmission of a CTS frame (i.e., an SU CTS frame) fromone STA may be elicited by a trigger frame. For example, if the UL MUPoll Confirm frame is a second type (e.g., SU RTS), one of the pluralityof STAs may transmit a SU CTS frame.

As described above, a trigger frame requesting CTS frames beforetransmission of a UL MU PPDU starts may be directed to a plurality ofSTAs requested for UL MU PPDU transmission (i.e., a first-type triggerframe) or one of STAs requested for UL MU PPDU transmission (i.e., asecond-type trigger frame).

Additionally, UL MU data transmission from a plurality of STAs may beelicited by a trigger frame. For example, if the UL MU Poll Confirmframe is the third type, a plurality of STAs may transmit data frames inUL MU. As illustrated in the example of FIG. 22, a plurality of STAs maybe requested to transmit a UL MU PPDU in immediate response to a triggerframe (e.g., immediately an SIFS after reception of the trigger frame),rather than they are requested to transmit CTS frames before they startto transmit a UL MU PPDU.

Also, UL random access transmission from one or more STAs may beelicited by a trigger frame. For example, if the trigger frame is thefourth type like a UL MU Poll Request frame, an STA may transmit a UL MUPoll Response frame in random access allowing collision.

In this manner, the AP may request or indicate different types of ULtransmission using a trigger frame (e.g., a UL MU Poll Confirm frame).That is, one of MU CTS transmission, SU CTS transmission, UL MU PPDUtransmission, and UL random access transmission may be performedaccording to information included in a trigger frame.

For this purpose, explicit information indicating the type of a triggerframe may be included in the trigger frame so that a UL transmissionscheme may be determined based on the information. Or trigger frametypes corresponding to trigger frames of a plurality of formats arepreset so that when a trigger frame of a specific format is received, aUL transmission scheme may be determined according to a trigger frametype corresponding to the format.

Or a new field indicating whether CTS transmission is requested may beadded to a trigger frame. Thus, whether a CTS frame is to be transmittedbefore transmission of a UL MU PPDU may be indicated. Or informationindicating the type of a CTS frame (e.g., information indicating MU CTSor SU CTS) may be added to a trigger frame. If the information does notindicate any CTS type (or the information is reserved), a UL MP PPDU maybe transmitted, not preceded by a CTS frame. Or a field indicatingwhether CTS transmission is requested and information indicating a CTStype (e.g., information indicating MU CTS or SU CTS) may be added to atrigger frame.

FIG. 23 depicts an exemplary method according to the present disclosure.

In step S2310, an AP may transmit a first trigger frame to an STA group(i.e., an STA group including one or more STAs). For example, the firsttrigger frame may correspond to a poll frame triggering UL MUtransmission or a UL MU Poll Request frame for UL MU random access.

In step S2320, each STA of the STA group may determine whether torespond to the first trigger frame based on information included in thefirst trigger frame. For example, if the first trigger frame correspondsto a poll frame triggering UL MU transmission and includes informationrequesting UL MU transmission to the STA receiving the poll frame, theSTA may determine to perform first UL MU transmission in response to thefirst trigger frame. Or if the first trigger frame corresponds to a ULMU Poll Request frame for UL MU random access, the STA receiving the ULMU Poll Request frame may determine whether to participate in UL MUrandom access based on whether a response condition for the UL MU randomaccess is satisfied.

An STA that has determined to respond to the first trigger frame in stepS2320 may perform the first UL MU transmission. For example, if thefirst trigger frame corresponds to a poll frame triggering UL MUtransmission, the first UL MU transmission may correspond totransmission of a UL MU PPDU including UL frames from a plurality ofSTAs. Or if the first trigger frame corresponds to a UL MU Poll Requestframe for UL MU random access, the first UL MU transmission may includea UL random access-based UL MU Poll Response frame. The UL randomaccess-based UL MU Poll Response frame may include informationindicating that the STA transmitting the UL random access-based UL MUPoll Response frame will participate in UL MU transmission. Or if theSTA transmitting the UL random access-based UL MU Poll Response frame isa TIM STA, the UL random access-based UL MU Poll Response frame mayinclude information requesting DL data transmission.

In step S2330, transmissions from all STAs participating in the first ULMU transmission from the STA group may end at the same time pointindicated by the first trigger frame. For this purpose, one or more ofthe STAs participating in the first UL MU transmission may add paddingsto their transmitted UL frames.

In step S2340, upon receipt of a UL frame from at least one STA of theSTA group performing the first UL MU transmission, the AP may determinethat frame exchange initiated by the first trigger is successful. Also,upon receipt of a UL frame without an error from at least one STA of theSTA group performing the first UL MU transmission, the AP may determineto transmit a response frame to the fist UL MU transmission.

In step S2350, the AP may transmit a DL MU frame to the STA group inresponse to the first UL MU transmission. The DL MU frame may include atleast one of a plurality of units for the plurality of STAs and anadditional trigger frame (e.g., a second trigger frame). Each of theunits for the plurality of STAs may include at least one of ACKinformation (e.g., a block ACK frame) for UL transmission from one ofthe plurality of STAs participating in the first UL MU transmission anda DL data unit for one of the plurality of STAs. In an embodiment, theDL MU frame may include block ACK information for the plurality of STAsand a second trigger frame. The ACK information or the second triggerframe that the AP transmits in response to the first UL MU transmissionmay be transmitted a specific IFS (e.g., an SIFS) after the ending timeof the first UL MU transmission (i.e., the ending time of the first ULMU transmission, indicated by the first trigger frame). Also, the ACKinformation for the first UL MU transmission and the second triggerframe may be included in one frame and thus simultaneously transmitted.If the first UL MU transmission includes information requesting DL datatransmission from TIM STAs, the AP may transmit DL data in response tothe information. The DL data may be transmitted in a DL MU PPDU to aplurality of TIM STAs.

In step S2360, only when the frame transmitted in response to the firstUL MU transmission by the AP in step S2350 includes a second triggerframe, second UL MU transmission may be performed. That is, an STA thathas received the second trigger frame in step S2350 may determinewhether UL MU transmission is requested to the STA. If UL MUtransmission is requested to the STA, the STA may participate in thesecond UL MU transmission.

FIG. 24 depicts another exemplary method according to the presentdisclosure.

In step S2410, an AP may transmit a trigger frame to an STA group (i.e.,an STA group including one or more STAs). The trigger frame may be afirst, second, third, or fourth type. Explicit information indicatingthe type of the trigger frame may be included in the trigger frame, orthe type of the trigger frame may be implicitly indicated according to apredetermined format. Also, the trigger frame may be a first or secondtrigger frame in the example of FIG. 23.

In step S2420, upon receipt of the trigger frame, an STA may determinewhether to respond to the trigger frame by NAV check. For example, ifthe STA determines that a channel is busy by the NAV check (e.g., a NAVvalue is a non-zero value), the STA may not respond to the trigger framein step S2430. Or if the STA determines that the channel is idle by theNAV check (e.g., the NAV value is not a non-zero vale), the STA maydetermine to respond to the trigger frame in step S2440.

In step S2440, the STA receiving the trigger frame may determine whetherthe trigger frame requests a first-version response frame or asecond-version response frame. The first version may be an older versionthan the second version. More specifically, the first version maycorrespond to a legacy PPDU format such as a non-HT version, and thesecond version may correspond to a HE PPDU format. If the first-versionresponse frame is requested, the STA proceeds to step S2450 andotherwise, the STA may proceed to step S2460.

In step S2450, if the trigger frame indicates one STA, the one STA maytransmit a first-version response frame in step S2451. If the triggerframe indicates one STA and does not include resource allocationinformation, the one STA may transmit the first-version response frame.In this case, the trigger frame corresponds to the afore-describedsecond-type trigger frame. The STA indicated by the second-type triggerframe may transmit the first-version response frame (e.g., an SU legacycontrol frame, specifically a legacy CTS frame) elicited by thesecond-type trigger frame in UL SU.

If the trigger frame indicates one or more (e.g., a plurality of) STAs,not just one STA in step S2450, the one or more STAs may transmitfirst-version response frames in step S2452, as illustrated fromexchange between a UL MU Poll Confirm frame and a CTS frame in FIG. 22.If the trigger frame indicates one or more STAs and does not includeresource allocation information, the one or more STAs may transmitfirst-version response frames. In this case, the trigger framecorresponds to the afore-described first-type trigger frame. Also, thefirst-type trigger frame may be multicast or broadcast. If thefirst-type trigger frame is multicast, the first-type trigger frame mayindicate one group of STAs. If the first-type trigger frame isbroadcast, the first-type trigger frame may indicate all STAs receivingthe trigger frame. The one or more STAs indicated by the first-typetrigger frame may simultaneously transmit first-version response frames(e.g., MU legacy control frames, specifically MU CTS frames) elicited bythe first-type trigger frame in UL MU transmission. The whole or part ofthe first-version response frames may be transmitted in the sameresources corresponding to shared resources. The same resources mayrefer to partially or fully identical time, frequency, and spaceresources.

On the other hand, if the trigger frame indicates one or more STAs(e.g., dedicated resources are explicitly or implicitly allocated for ULtransmission of one or more STAs) in step S2460, the one or more STAsmay transmit second-version response frames in the allocated resourcesas illustrated from exchange between a UL MU Poll Confirm frame and a ULMU PPDU frame in FIG. 21, in step S2461. In this case, the trigger framecorresponds to the afore-described third-type trigger frame. The one ormore STAs may simultaneously transmit second-version response frames(e.g., UL MU frames, specifically UL MU data frames) elicited by thethird-type trigger frame in UL MU transmission.

If the trigger frame does not indicate one or more STAs and allowstransmission of an STA unspecified by the AP in step S2460, one or moreunspecified STAs may transmit second-version response frames asillustrated from exchange between a UL MU Poll Request frame and a UL MUPoll Response frame in FIGS. 18 and 19, in step S2462. The one or moreSTAs may participate in UL MU transmission using random access resourcesallowing collision. In this case, the trigger frame corresponds to theafore-described fourth-type trigger frame. The one or more STAs maysimultaneously transmit second-version response frames (e.g., UL MUframes, specifically UL MU data frames) elicited by the fourth-typetrigger frame using random access resources allowing collision.

As described above, a different UL transmission scheme or a different ULtransmission frame type may be determined according to the type of atrigger frame.

While the exemplary method has been described with reference to FIG. 23or FIG. 24 as a series of operations for simplicity of description, thisdoes not limit the sequence of steps. When needed, steps may beperformed at the same time or in a different sequence. All of theexemplary steps are not always necessary to implement the methodproposed by the present disclosure.

The foregoing embodiments of the present disclosure may be implementedseparately or combinations of two or more of the embodiments may beimplemented simultaneously, for the method of FIG. 23 or FIG. 24.

The present disclosure includes an apparatus for processing orperforming the method of the present disclosure (e.g., the wirelessdevice and its components described with reference to FIGS. 1, 2, and3).

The present disclosure includes software (an operating system (OS), anapplication, firmware, a program, etc.) for executing the method of thepresent disclosure in a device or a computer, and a medium storing thesoftware that can be executed in a device or a computer.

While various embodiments of the present disclosure have been describedin the context of an IEEE 802.11 system, they are applicable to variousmobile communication systems.

What is claimed is:
 1. A method for transmitting a plurality of uplinkframes by a station (STA) to an access point (AP) in a wireless localarea network, the method comprising: receiving from the AP a firsttrigger frame for eliciting a first uplink Multiple User (MU)transmission from a plurality of STAs, the plurality of STAs includingthe STA; transmitting to the AP a first uplink frame, wherein the uplinkframe is transmitted in the first uplink multiple user (MU)transmission; receiving from the AP a frame in response to the firstuplink MU transmission a predetermined time after an end of the firstuplink MU transmission, wherein the frame received in response to thefirst uplink MU transmission includes acknowledgment (ACK) informationfor the first uplink MU transmission and a second trigger frame foreliciting a second uplink MU transmission, the second trigger frameincluding scheduling information for the second uplink MU transmission;and transmitting to the AP a second uplink frame, wherein the seconduplink frame is transmitted in the second uplink MU transmission.
 2. Themethod according to claim 1, wherein the STA receives the frame inresponse to the first uplink MU transmission a SIFS (Short Inter-FrameSpace) time after the end of the first uplink MU transmission.
 3. Themethod according to claim 1, wherein the AP determines that the firstuplink MU transmission is successfully received when the AP receives anuplink frame from at least one STA among the plurality of STAs as partof the first uplink MU transmission.
 4. The method according to claim 3,wherein the frame received in response to the first uplink MUtransmission is transmitted by the AP when a physical layer of the APindicates that an uplink frame from at least one STA among the pluralityof STAs is received with no error.
 5. The method according to claim 1,wherein the STA transmits the second uplink frame in response toreceiving the second trigger frame.
 6. The method according to claim 1,wherein an ACK policy of the STA is set to Immediate Block ACK.
 7. Themethod according to claim 1, wherein ACK policies of the plurality ofSTAs are set to a same value.
 8. The method according to claim 1,wherein the first trigger frame includes response condition informationused by the STA for determining whether to transmit the first uplinkframe in response to the first trigger frame.
 9. The method according toclaim 8, wherein the response condition information indicates that aTraffic Indication Map (TIM) STA is allowed to transmit the first uplinkframe in response to the first trigger frame.
 10. The method accordingto claim 9, wherein the first uplink frame transmitted by the STA thatis a TIM STA indicates that the STA requests a downlink frame for theSTA buffered at the AP, the frame received in response to the firstuplink MU transmission includes the downlink frame for the STA bufferedat the AP, and the downlink frame is included in a downlink MU Physicallayer Protocol Data Unit (PPDU).
 11. The method according to claim 8,wherein the response condition information indicates that a STA havingan uplink traffic having a specific access category is allowed totransmit the first uplink frame in response to the first trigger frame.12. The method according to claim 1, wherein the STA checks a networkallocation vector (NAV) before transmitting the first uplink frame, andtransmits the first uplink frame when a channel is idle according to theNAV.
 13. The method according to claim 1, wherein the STA transmits thefirst uplink frame including a control frame in the first uplink MUtransmission when a type of the first trigger frame is a first type. 14.The method according to claim 13, wherein the STA transmits the firstuplink frame including a data frame in the first uplink MU transmissionwhen the type of the trigger frame is a second type.
 15. A method forreceiving a plurality of uplink transmissions by an access point (AP) ina wireless local area network, the method comprising: transmitting afirst trigger frame for eliciting a first uplink transmission from oneor more stations (STAs); receiving from the one or more STAs the firstuplink transmission; transmitting a response frame in response to thefirst uplink transmission a predetermined time after an end of the firstuplink transmission, wherein the response frame includes bothacknowledgment (ACK) information for the first uplink transmission and asecond trigger frame for eliciting a second uplink transmission, thesecond trigger frame including scheduling information for the seconduplink transmission; and receiving the second uplink transmission. 16.The method of claim 15, wherein the one or more STAs includes aplurality of STAs and the first uplink transmission is a first uplinkMulti-User (MU) transmission.
 17. The method of claim 16, wherein thesecond uplink transmission is a second uplink MU transmission.
 18. Themethod according to claim 15, wherein the first trigger frame includesresponse condition information used by a STA of the one or more STAs fordetermining whether to transmit an uplink frame in response to the firsttrigger frame, and the response condition information indicates that aTraffic Indication Map (TIM) STA is allowed to transmit the uplink framein response to the first trigger frame.
 19. The method according toclaim 18, wherein the uplink frame transmitted by the TIM STA indicatesthat the TIM STA requests a downlink frame for the TIM STA buffered atthe AP, wherein the response frame includes the downlink frame for theTIM STA buffered at the AP, and wherein the downlink frame is includedin a downlink Multi-User (MU) Physical layer Protocol Data Unit (PPDU).20. The method according to claim 18, wherein the response conditioninformation indicates that a STA having an uplink traffic having aspecific access category is allowed to transmit the uplink frame inresponse to the first trigger frame.